USVI Public Records

Document text

This is a digital copy of a book that was preserved for generations on library shelves before it was carefully scanned by Google as part of a project to make the world’s books discoverable online. It has survived long enough for the copyright to expire and the book to enter the public domain. A public domain book is one that was never subject to copyright or whose legal copyright term has expired. Whether a book is in the public domain may vary country to country. Public domain books are our gateways to the past, representing a wealth of history, culture and knowledge that’s often difficult to discover. Marks, notations and other marginalia present in the original volume will appear in this file - a reminder of this book’s long journey from the publisher to a library and finally to you. Usage guidelines Google is proud to partner with libraries to digitize public domain materials and make them widely accessible. Public domain books belong to the public and we are merely their custodians. Nevertheless, this work is expensive, so in order to keep providing this resource, we have taken steps to prevent abuse by commercial parties, including placing technical restrictions on automated querying. We also ask that you: + Make non-commercial use of the files We designed Google Book Search for use by individuals, and we request that you use these files for personal, non-commercial purposes. + Refrain from automated querying Do not send automated queries of any sort to Google’s system: If you are conducting research on machine translation, optical character recognition or other areas where access to a large amount of text is helpful, please contact us. We encourage the use of public domain materials for these purposes and may be able to help. + Maintain attribution The Google “watermark” you see on each file is essential for informing people about this project and helping them find additional materials through Google Book Search. Please do not remove it. + Keep it legal Whatever your use, remember that you are responsible for ensuring that what you are doing is legal. Do not assume that just because we believe a book is in the public domain for users in the United States, that the work is also in the public domain for users in other countries. Whether a book is still in copyright varies from country to country, and we can’t offer guidance on whether any specific use of any specific book is allowed. Please do not assume that a book’s appearance in Google Book Search means it can be used in any manner anywhere in the world. Copyright infringement liability can be quite severe. About Google Book Search Google’s mission is to organize the world’s information and to make it universally accessible and useful. Google Book Search helps readers discover the world’s books while helping authors and publishers reach new audiences. You can search through the full text of this book on the web at http://books.google.com/ aS 3 OR P aa) VIN ESEAN £15 NT rag ve aaoeat mt Oy, EMTIAE (ER TAS J RAI TY O wit 2) (3 1 ae Waies ~~ ace ars Se to ma Hosted by Goog le ie NX Hosted by Google 6 os ae . “” ee fe fe a % Ms ie 2 s db Goo be ey a - 4 ke 2B gle Dk ee ve os Hosted by Google Hosted by Google NEW YORK ACADEMY OF SCIENCES SCIENTIFIC SURVEY OF Porto Rico and the Virgin Islands VOLUME I NEW YORK: ISHED RY TH 1 1 . aohag ‘ t Hosted by Goog le CONTENTS OF VOLUME I Tage Title-page 2... ccc cee eee ce teen cece eee ee ee eee ee teen eens i Contents co.cc ccc cece ccc eee eee eee eee cee eee teen ee eee eee terete eee eeees iii Dates of Publication of Parts... ..... 0... cece cece eee eee tenes iii List of Tllustrations... 0.0.0... 6 cece cc cee cece cece cree tee eenee iv EVvata cece ccc ce cee eee eee ee eee ee een ee eee een eee eee eeee vii History of the Survey. By N. Ll. BRITTON........... 00. cece eee eee eee 1 Introduction to the Geology of Porto Rico. By CHar Les P. BERKEY..... VW New Base Map of Porto Rico. By CHESTER A. REEDS...............0.- 30 Geology of the San Juan District. By Dovetas R. SEMMES............ 33 Geology of the Coamo-Guayama District. By Epwin T. Hopce.......... 111 Geology of the Ponce District. By GraHam J. MITCHELL............... 229 The Physiography of Porto Rico. By ARMIN K. LOBECK................ 301 UBC (> 381 DATES OF PUBLICATION OF PARTS Part 1, September 26, 1919. Part 2, May 25, 1920. Part 3, Mareh 1, 1922, Part 4+, December 20, 1922. (ili) iv SCIENTIELG SURVEY OF PORTO RICO LIST OF ILLUSTRATIONS PLATES Page I. Block Diagram of the San Juan District, P. Reo... oe. eee eee ee eee. 42 Il. Fauna of the Arecibo Formation. . 0.0.0.0... 66. ce ee eee DS Itt. Foraminifera ...........-.455. Pe eee ee ent eee ee 74 TV. Geologic Cross-section... 6... cence ee LOG Vv. Generalized Geological Cross-section of Ponce District 262 VI. Generalized Geological Cross-section of Ponce District 264 VIL. Generalized Columnar Section of Ponce District...............% 20. 268 Figures Page Diorite porphyry SHIS...........--..e eee a 20 Detail of the double structure in the San Juan formation at Arecibo..... 21 Haystack (pepino) bills... 0.6... eee eee ee eee eee eee eee py Valley of the Plata, just below the power dam at K 19, Comerio Road.... 39 San Juan consolidated dune sand forming fringing islands at Vega Baja PIAVA coc en een enn e nents 43 The playa plains near Arecibo... 6.66. cee eee nee eee 44 Typical haystack topography as developed in the western portion of the San Juan District... ee eee eee . 45 Section through the Arecibo formation... 0.00... 0606 eee eee eee 47 Inface of cuesta and inner lowland near Corozal... 2.6... eee eee 48 The inner lowland and the inface of the cuesta at Corozal....... 6... eee. AY Morro castle and a portion of the city of San Juan, built upon a promon- tory composed of the San Juan consolidated lime sand...............- 33 San Juan consolidated lime sands... . cc ee ee ee eee eee ot Exfoliation producing concentric arrangements in ash beds south of Bayamon oo... ce eee eee e een e eee 62 Crumpling due to solifluction in the Juan Ascencio chert...............- 66 Typieal foraminiferal shale... 6. ee eens 6S Chart showing the relative positions of the principal foraminiferal beds... 73 Diorite porphyry sills intruded between liyers of shales and ashes at K 20. Comerio Road... oc eee eee eee eee teas v7 Faulted trachyte dike crossing the La Plata River... .................4.. 7s Photomicrograph of vitrophyr occurring north of Cidra................. 80 Rhyolite porphyry... ee ee eee eee eee 82 Soda granite. showing poikilitic structure... 0.0.0.0... . 00. ce ee ee eee Sh Soda granite occurring south of Naranjito...........0 0.0... 0.0...0.000. S4+ Quartz diorite... eee etc eee eee 86 Trachyte, showing poorly developed trachytic structure, crossed nicols... ST Latite, showing veins filled with epidote and iron oxides................ SS An andesite porphyry with large phenocrysts of plagioclase surrounded by an groundmass, showing the structure of a natural slag............0.. S9 Andesite porphyry impregnated with chrysocolla. Barrio Pasto......... 00 CONTENTS OF VOLUME J \ Page Diorite porphyry with pyroxene phenocrysts in a groundimass of lath- shaped feldspars (plagioclase)....... 065... ce eee eee ence eee ot Olivine basalt.. Se ee ee ee ee ee ee ee eee eee eee eee teen e eee oz Gross-bedded structur e in the San Juan formation at Arecibo........... OF Block diagram of Coastal Plain... 0... 0.2... cece eee eee 117 Guayama upon the upper coastal terrae ee ee ee eee te eee eee eee 11S Cayey in the Barranquitas-Cayey Lowland... ......2....65. 0. eee eee eee 121 Tutt DCIS... cc cc cee ce eee eee eee tee eee nee e eens vee eee -131 Lithocampe sp. in shales of the Barranquitas-Cayey series.............- 135 Shells worn, oxidized, and cemented together to form one of the lime- stones of the Barranquitas-Cayvey series... 6... cc ee ce eee 15 Topography of the Barranquitas-Cayey Lowland...............++2.+-0-- 136 Character of the unconformity between the Barranquitas-Cayey and the Sierra de Cavey Series. 2... cece ee ete ete eee 13S Conglomerate with an igneous matrix... 2.60.06. ee ee eee eee 14) Ash shales containing Orbitolites . 144 Chert with desiccation fractures 145 Crystal tuff.. 146 Lithic tuff...... 11 Comno Springs limestone exposed in the Descalabrados Gap...........0. 14 Lithothamiion thallus in cross-section in the Coamo Springs limestone... 155 Lithothamnion thallus in longitudinal section in Coamo Springs limestone 156 St Coamo Springs Range..........6..05 Bec ee ce ec eee eee cece ee ete naas 157 Lithothamnion in Coamo Springs limestone... ... 0.0.0.0... eee ee eee 158 Amphistegina in Coamo Springs limestone.......0. 00.6... ee eee ee eee .. 160 Porodiseus concentricus in shales... cee eee 162 Shales of the Rio Desealabrados series... 0.0.6.0... eee cee ee eee 163 Valley of the Guamanti........ ee eee De eee wee ene beer e teehee eee taees 16S Cerro Gavias, Coastal Terrace, Coamo River. soo... 0.0.0.2 cee cee eee 169 Felspathic andesite... 0... 6. ccc eee eee eee ce eee eens 172 Augite andesite... .. 0.0... ee eee eee see e ee eee eee ee eee tee eee e eens 174 Augite andesite showing feldspars completely altered; augites unaltered... 175 Glassy-augite andesite... 0... cee cece ee cee eee eee e eens 176 Olivine andesite... 0.0... 0... eee eee eee 17 Olivine free basalt............. : 17° Olivine basalt........ sees rare See eee eee eee cece e eee 179 Lava flow containing pyroclasts of ealeite which are surrounded by garnets 181 Flow breccia... .. ee eee eee ee sees whew es ee ee weweeees beeen eee 182 [gneous structure of the Sierra de Cayey conglomerate matrix.......... Ish Relation of isothermal surfaces to andesitic columns.................00. 1s4 Hornblende granite... 0.2.0... cee ce cee eee eee eee e eee ne es 186 Biotite granodiovite. .. 0.00.0 cc ee ee eee e eter eee ee eee 1ST Hornblende diovite.. 0.0.0... cece eee eee e en een tebe nent eee 1S Hornblende-augite diorite... 0.0.0... c cc ce eee tee e ence renee Tso Hornblende andesite... 0.0.0... ee eee eee tence eee beeen nee 190 Hornblende-augite andesite... 0.6... ccc eee eee eee eee eee eees 191 Porodiscus concentricus in tuffaceous shale... 6.0.0... 0. eee ee eee 195 “Llobigerina and alge in the Coamo Springs limestone.................. 195 Vi SCIENTIFIC SURVEY OF PORTO RICO Page Chlorite developing from feldspars which are associated with fresh augites 208 Epidote replacing feldspars....... 66... . cece cece cence eee eee teen eens 204 Minerals named in order from the center outwards: stained antigorite, stilbite, laumontite, and calcite.......... Lovee cece ec eer ceeserceseeces 205 Intimate mixture of quartz, epidote, and actinolite.............-.....45- 206 Quartz and epidote replacing feldspar...........-- +++ seer eee eee ee eens 207 Spherulitic growths of specular hematite and ehalcedony....... 6... seco 208 Coamo Springs.........0 cece eee cence eee ene eee e eee een e ten eeee 210 Barrio del Carmen Prospect...... 00... cece eee e terete eee eeeeeeeeeee 221 Portion of Complex mountain province as seen from the Tertiary hills Cuspated beach, west coast, Porto Rico, just south of Melones Point..... 246 Fluted Guayabal limestone of Juana Diaz......... 6... cee ee eee eee 256 Rio Yauco shale, as seen from point one mile north of kilometer 15.0, Yauco-Lares road... ce ccc ccc cece eee eee ee eee tenet eee eee eee e tenes 268 Faulted shale at kilometer 14.3, Yauco-Lares road......... 02.0.0 cee eeee 266 Augite porphyrite showing zoned augite crystal set in fine-grained ground- IMASS cece cece cence cree eee eee eee n seen eeeees dee wee we eee e erent tanaes 274 Clypeaster rosaceus, Lamark... 6... eee eee eee cence eens 284 Hemiaster berkeyi n. sp., Jackson. X 3/2... 0.0... e eee ee eee 286 “Montalva” Salina, west of Guanica, on south coast.............-.65-0- 296 Map showing the average annual rainfall in Porto Rico................. 3038 Sketch map of Porto Rico showing regions visited................5 eee 304 Map of Porto Rico showing the chief physiographic regions............. 304 The main stages in the physiographic development of Porto Rico........ 305 Block diagram of the southwest corner of Porto Rico...............205- 311 Appalachian ridge structure in the oldland rocks between Boqueron and DP a Cc) 312 Valley of the Manati River above Ciales......... 66. cece ee cee eee eee eee 3138 The valley and flood plain of the Rio Grande de Loiza near Carolina..... 317 North-south profile through Porto Rico.......... 6. eee ec ee cee eee eee 318 Diagram of the Guanica district... 0.0.0.0... cece cece ee eee eens 318 The inner lowland at Guanica......... cc eee ee eee eens 321 The inner lowland at Guanica..... 0.0... cece ee eee ee eee eet enee 322 Basal Tertiary south of Yauco, along the Guanica road................. 826 The gorge of the Manati, incised below the surface of the coastal plain... 330 Open haystack belt between Barceloneta and Arecibo...........-...006. 335 Apparent wave-cut bench at Quebradillas............ 02. 0c cece eee eee 3386 The inner lowland of the south coast, looking eastward from cuesta face back Of PONG... 6... ce cece cee eee ee eee eee cette teen eens OBS The Tertiary coastal plain lapping upon southern flank of Mariquita Hill. 339 The surface of the coastal plain between Ponce-and Penuelas............ 340 Beds of the coastal plain dipping slightly toward the oldland............ 341 Road cut at K 9 H9 on the Ponce-Pefiuelas road, showing relation of Ter- tiary to older series... . 6. cc ce ce eee ee eee eee eee een e tenes 342 Section of hill along Jacaguas River one mile southwest of Juana Diaz.. 3438 The drowned coast of eastern Porto RicO...... 0... eee eee eee eee 345 Lower course of the Descalabrado River during the dry season.......... 350 CONTENTS OF VOLUME I Vil Page. The high terrace of the Plata River at K 13 on the Comerio road........ 351 Alluvial terraces of the Pefia Pobre Creek, west of Rio Blanco crossing... 352 Tidal deltas at Luquillo..... 0... cee e eee eee e eens 354 Sketch map of the coast of Luquillo.............. 0. cece cece eee ee eee 354 Tidal flats just east of Point Embacaderos............ 0 cee eee cee eee e eee 355 Wave action along joint plane, San Juan Point.....................000. 356 The Caribes Islands..... 0... ccc eee cece ce ee eee eee eee ete ee tet tee B57 The low southward sloping coastal plain east of Cape Rojo.............. B58 The marine cliff forming the edge of the Tertiary coastal plain on the north coast west of Isabela... . 2.0... ccc cece eee ee eect ee eens BOA North-south profiles through the margin of the coastal plain at Quebra- dillas and Isabela... 0.00. cece ee eee tee eee eee teen ene e tens 360 River mouths at the north coast....... 2... cece eee eee eee 862 The coast east of Quebradillas. 0... 0... cece ee eee eee e eee 365 The uplifted beach on the south side of Desecheo Island................ 367 The uplifted beach on Muertos Island......... 00... cece eee eee 369 Bast coast of Mona Island... ... cc cece ce ee ee eee eee teens 372 Sketch of Culebra and Vieques Island...... 0.0... cece eee ee eee eee 3BT4 Muertos Island from the north....... 00... ee eee eee eee eee eee BId Mars Outline Map of Porto Rico showing distribution of district studies....... 26 New Base Map of Porto Rico, Compiled from the latest Government SOULCES 2... cece ee ce eee eee eee eee ee enter tere teen ene ee eee 30 Geologic Map of the San Juan District, Porto Rico. Geologic Map of the Coamo-Guayama District, Porto Rico. Geologie Map of the Ponce District, Porto Rico. Physiographic Map of Porto Rico. ERRATA Page 58, line 83, and page 59, line 8, read J/etis for Metris Hosted by Google NEW YORK ACADEMY OF SCIENCES SCIENTIFIC SURVEY OF Porto Rico and the Virgin Islands VOLUME I—Part 1 History of the Survey—N. L. Britton Geological Introduction—C_P. Berkey Geology of the San Juan District—D. R. Semmes f Fos Pees fo 45 nee NEW YORK: PUBLISHED BY THE ACADEMY 1919 Hosted by Google HISTORY OF THE SURVEY By N. L. Brrrron CHAIRMAN OF THE COMMITTEE In the latter part of the year 1913, subsequent to a discussion in the Council of the Academy relative to proposed extensions of the Acad- emy’s ordinary activities, a proposition for a scientific survey of Porto Rico was approved and referred to a committee consisting of Professors Boas, Britton, Crampton, Kemp and Poor, at the meeting of the Council in November of that year, at which meeting the Council appropriated $500 annually for five years for the purposes of this investigation. Dr. E. O. Hovey and Dr. R. W. Tower, Recording Secretaries of the Acad- emy, have acted with the Committee. Professor Charles P. Berkey suc- ceeded Professor Kemp as a member of the Committee in 1917. Mr. Emerson McMillin, at that time President of the Academy, kindly offered to assist the work, and has contributed $3,000. The Porto Rico Govern- ment was also interested in the investigation, and has since made two appropriations of $5,000 for prosecuting the work. The codperation of The American Museum of Natural History, The New York Botanical Garden, scientific departments of Columbia University and other institu- tions was secured, and both field-work and the study of the collections made has progressed almost continuously. The cooperating institutions already had some collections from Porto Rico. The two agricultural ex- periment stations of Porto Rico, one at Mayaguez and one at Rio Piedras, have also aided the investigation. A number of preliminary papers deal- ing with special phases of the work have been published. The publica- tion of the final reports of the survey is herewith commenced and will be continued in the following sequence: geology, paleontology, botany, zoology and anthropology. Professor, Crampton proceeded to Porto Rico at the end of 1913 and carried out a zodlogical reconnaissance, traveling over a large part of the island, and discussed the plan with officials of the Insular Government. He subsequently published an account of Porto Rico. In January, February and March, 1914, Dr. J. A. Shafer prosecuted botanical exploration on the island Vieques, one of the small islands + Am. Mus. Jour., XVI, pp. 59-70. 2. SCIENTIFIC SURVEY OF PORTO RICO politically a part of Porto Rico, and made the first representative col- lection of plants obtained on that island.? During February and part of March, 1914, Dr. Britton, accompanied by Mrs. Britton, Mr. John F. Cowell and Dr. Frank E. Lutz, made bo- tanical and entomological collections in the northern and western parts of Porto Rico and in the smal] islands Desecheo and Mona, which yielded several thousand specimens and much information. Dr. Britton con- tributed to the twenty-fifth anniversary celebration of the Missouri Botanical Garden a paper on The Vegetation of Mona Island.* In the summer and autumn of 1914, zodlogical collections were made over considerable portions of the island by Messrs. Roy W. Miner in marine invertebrates and myriopods, John T. Nichols in fishes, and Frank FE. Watson and H. G. Barber in insects and arachnoids. Many thousand specimens were obtained and important additions were made to the knowledge of these groups of animals. The spiders of this col- lection, taken with those previously obtained by Professor Crampton and Dr. Lutz, yielded important information, which was utilized by Dr. Lutz in his List of Greater Antillean Spiders, with Notes on Their Distribu- tion.* Nichols has published some of the results of his work wnder the title Fishes New to Porto Rico.’ The geological investigation was commenced by Dr. Charles P. Berkey and Dr. Clarence N. Fenner, who spent parts of August and Septem- ber, 1914, in a reconnaissance and laid a substantial foundation for sub- sequent studies. Professor Berkey has published an illustrated account of this reconnaissance under the title Geological Reconnaissance of Porto Rico.® In July and August, 1914, Dr. J. A. Shafer devoted about six weeks to the study of the forests of the Sierra de Naguabo, and added a num- ber of species of plants to the known flora of Porto Rico. Under the auspices of the New York Botanical Garden, Professor N. Wille, Director of the Botanical Garden at Christiania, Norway, spent the period from the latter part of December, 1914, until the end of March, 1915, in collecting and studying the fresh-water and aerial algw~ over considerable areas of the island. He obtained many thousand speci- mens of these organisms, which proved to be more abundant there than * Jour. N. Y. Bot. Gard., XIV, pp. 103-105. ® Ann, Mo. Bot. Gard., II, pp. 33-58, Pls. I, II. (Contributions from N, Y. Bot. Gard., No. 175.) 4Ann. N. Y. Acad. Sci., XXVI, pp. 71-148. 5 Bull, Am. Mus, Nat. Hist., XXXIV, pp. 141-146. SAnn. N. Y. Acad. Sci., XXVI, pp. 1-70. (Contributions from Dept. of Geology, Co- lumbia Univ., Vol. XXV, No. 20.) 7 Jour, N, Y. Bot. Gard., XVI, pp. 33-35. BRITTON, HISTORY OF THE SURVEY 3 had hitherto been supposed. This collection has not yet been critically studied, but Professor Wille is confident that it contains some unde- scribed genera and numerous undescribed species. Since his return to Norway, subsequent to the expedition, Professor Wille has been much occupied with administrative duties, but it is hoped that he will yet find time to enumerate and describe the elements of this rich collection, the first comprehensive one that has been made of these minute alge within the American tropics. He has published a narrative report of his field- work.® The greater portions of the months of February and March, 1915, were spent by Dr. Britton, Mrs. Britton, Mr. John F. Cowell and Mr. Stew- ardson Brown in continuing botanical exploration, especially in western and southwestern portions of Porto Rico, including a study of the coasts from Mayaguez south to Morrillos de Cabo Rojo and westward to Ponce and Cayo Muertos. Large collections were obtained, which added much to the knowledge of the geographical distribution of the flora, and a series of rock specimens were collected and turned over to the geologists of the survey for examination.® Based on the observations made on this and preceding trips, Dr. Brit- ton outlined a plan of forest policy for the Porto Rican Government, which he presented at the spring meeting of the National Academy of Sciences, held at Washington in April, 1915, and it was transmitted to the Governor of Porto Rico. The reforestation of Porto Rico is acutely necessary. A recent report on the forests of Porto Rico by Mr. Louis 8. Murphy, Forest Examiner of the United States Forest Service, is of great value in this connection.?° Dr. Chester A. Reeds and Mr. Prentice B. Hill devoted the months of June and July, 1915, to paleontological studies and collections in the western part of the island, obtaining over 10,000 specimens rich in fossil corals and fossil mollusks. They detected a stratum containing large quantities of fossil leaves; this noteworthy discovery, supplemented by further collections subsequently made by Mr. Bela Hubbard, gives us the first knowledge of the Tertiary flora of the West Indies. The collections of fossil plants made by Messrs. Reeds and Hubbard are being studied by Dr. Arthur Hollick. Dr. Reeds has published three maps. He discov- ered remains of a new fossil Sirenian, which has been described by Dr. W. D. Matthew." § Jour. N. Y. Bot. Gard., XVI, pp. 132-146. * Jour. N. Y. Bot. Gard., XVI, pp. 103-112. 1 Bull. U. S. Dept. Agric., 1916, No. 354, p. 99. 1 Ann. N, Y, Acad. Sci., XXVII, pp. 23-29. 4 SCIENTIFIC SURVEY OF PORTO RICO Mr. Edwin T. Hodge spent the summer and early autumn of 1915, first, in an investigation of the supposed petroleum oil shales in the west- ern part of the island, obtaining samples from 26 different localities, and later in the year submitted a report upon them, which gave negative re- sults, Mr. Hodge concluding that oil-carrying shales do not exist in Porto Rico. Mr. Hodge subsequently made a detailed geological study of the Coamo region, and his results have been made ready for publication. He also made a study of the thermal springs of the island, especially those of Bafios de Coamo. Mr. D. R. Semmes prosecuted geological investigations of the section of the north central portion of the island, which, taken with the work of Mr. Hodge to the south, furnishes data for a complete geological cross-section from coast to coast. The studies of Mr. Semmes are pub- lished herewith. Mycological studies and collections were made from June to August, 1915, by Professor F. L. Stevens, in continuation of similar investiga- tions prosecuted by him while Dean of the College of Agriculture at Mayaguez. He visited nearly all parts of the island and collected many thousand specimens; his trip was under the auspices of the University of Illinois and of the New York Botanical Garden.’? Professor Stevens described and illustrated the species of the large genus Meliola as repre- sented in Porto Rico, under the title The Genus Meltola in Porto Rico, which includes descriptions of sixty-two new species and varieties.!* Professor Crampton continued zodlogical field-work during January, 1915, especially in the northwestern portion of the island, at which time he supplemented previous collections by obtaining large numbers of specimens in the various groups of invertebrates. In the spring and early summer of 1915, Dr. Frank E. Lutz and Mr. A. J. Mutchler made extensive entomological collections in various parts of the island, adding some 15,000 specimens of insects and large nam- bers of spiders to collections previously made. Mr. Roy W. Miner and Mr. H. Mueller spent several weeks in the summer in the study and col- lection of marine invertebrates, especially in the vicinity of Guanica, some 8,000 specimens being obtained at that time from this region. Professor Raymond C. Osburn carried on studies of the organisms of the deeper waters in the vicinity of Guanica during the summer, obtaining over 2,000 specimens, principally by dredging. Professor Franz Boas prosecuted anthropological and archeological investigations at several points during May and June, 1915. aided by Dr. 12 Jour. N. Y. Bot. Gard., XVII, pp. 82-85. 8 Tllinois Biological Monographs II, No. 4, pp. 1-86, Pls. I-V. BRITTON, HISTORY OF THE SURVEY 5 Ul. K. Haeberlin, Dr. J. Alden Mason and Mr. Robert T. Aitken. Pro- fessor Boas obtained data which caused him to doubt the general assump- tion that children reach maturity earlier in tropical regions than in the temperate zone, and other data which are important as regards the hygi- ene of childhood in the tropics. His observations on the teeth of Porto Rican children have been published by Mr. Leslie Spier.1* He obtained cordial codperation in this investigation from the Department of Public Education of the island. He also concluded from his observations at this time that the Porto Rican race has been influenced in its development by environment. Professor Boas referred the collection of folk-lore data to Dr. J. Alden Mason, who prosecuted this study from June, 1915, until 1916, and accumulated an immense collection of folk tales, riddles, ballads and songs, which was subsequently referred for editing to Professor Aurelio M. Espinosa, of Leland Stanford University, whose work on this impor- tant contribution is now approaching completion, and who has reported to the Committee that the documents are the most important contribu- tion of its kind made to literature. Professor Espinosa and Dr. Mason have published Porto Rico Folk Lore—1. Riddles.*® Dr. Haeberlin made excavations in the Jobo district, including that of one stone enclosure and a cave, which contained ceremonial objects and large numbers of bones of an extinct mammal. A large cave in the vicinity of Utuado, excavated by Messrs. Mason and Aitken, proved to be the burial ground of an ancient community, and here also large numbers of bones of an extinct mammal were found.*° One of these mammals proved to be new to science, and has been described by Dr. J. A. Allen under the title An Extinct Octodont from the Island of Porto Rico, West Indies.17 Dr. Haeberlin has published a paper entitled Some Archeo- logical Work in Porto Rico.1® An ancient village site at Capa, located by Professor Boas and subse- quently investigated by Messrs. Mason and Aitken, proved to be the most important of all archeological localities thus far discovered in Porto Rico. Efforts were made by the Committee to induce the Porto Rico Government to purchase and preserve this site as a national monument, but hitherto without success. A preliminary description of the site has been given by Dr. Mason.1? 4 Am. Anthropologist, XX, pp. 37-48. % Jour. Am. Folk-Lore, NXIX, pp. 423-504. 16 XIX Congress of Americanists, pp. 224-228. Ann, N. Y. Acad. Sci.. XXVII, pp. 17-22, Pls. I-Y. 3 Am. Anthropologist, XIX, pp. 214-238. 1 XIX Congress of Americanists, pp. 220-223. 6 SCIENTIFIC SURVEY OF PORTO RICO Dr. Marshall A. Howe spent parts of June and July, 1915, in con-. tinuation of his previous studies of marine algw, principally along the southwestern coast from Ponce and Cayo Muertos to Cabo Rojo. During this trip he obtained about 3,000 specimens, including some species addi- tional to the known flora of the island.?° Professor Bruce Fink, of Miami University, proceeded to Porto Rico in November, 1915, and spent part of the winter there in making exten- sive collections of fungi and lichens. He has generously contributed information obtained by him to the Committee. Dr. Herbert J. Spinden prosecuted archeological work at several points during the spring and summer of 1916 and made extensive collections, the study of which yielded interesting and valuable information. He excavated certain shell heaps and obtained specimens and information therefrom, which he regarded as throwing light upon the origin of Porto Rican aborigines. He also studied the aboriginal petroglyphs or rock- carvings. Mr. Bela Hubbard carried out a geological survey of the northwestern section of the island in the summer of 1916, and his description of this work is in process of completion for publication. Dr. Charles R. Fettke studied the southwestern districts of the island in an areal geological survey, which included a detailed study of the extensive areas of eruptive rocks. The study of the large collections made by him is progressing. Mr. A. K. Lobeck studied, during the latter part of 1916 and January, 1917, the physiography of the entire island, and the results of this inves- tigation are prepared for publication. During the summer of 1916, a very important study of the parasitic fungi of Porto Rico was made by Professor H. H. Whetzel, of Cornell University, and Dr. E. W. Olive, of the Brooklyn Botanic Garden, aided by a grant from the New York Botanical Garden, and several thousand specimens of these plants were obtained, which are under investigation by a number of different experts. Mr. H. E. Anthony prosecuted studies of recent and fossil mammals in Porto Rico during the summer of 1916, and made some highly inter- esting and important discoveries, which have been described by him in three illustrated papers: Preliminary Report of Fossil Mammals from Porto Rico.” Preliminary Diagnosis of an Apparently New Family of Insectivores.?2 0 Jour. N. Y. Bot. Gard., XVI, pp. 219-225. a Ann, N. Y. Acad. Sci.. XXVII, pp. 1938-2038. He 2 Bull. Am, Mus. Nat, Hist., XXXV, pp. 725-728. BRITTON, HISTORY OF THE SURVEY q New Fossil Rodents from Porto Rico, with Additional Notes on Flas- modontomys obliquus Anthony and Heteropsomys insulans Anthony.** During the progress of the survey, Dr. John A. Stevenson, of the Insular Experiment Station at Rio Piedras, has made botanical collec- tions in various parts of the island, which have contributed much to our knowledge of the flora; he is now preparing a list of the fungi of Porto Rico. Dr. Basil Hicks Dutcher, U. 8. A., stationed at San Juan, has given valuable aid to nearly all our field parties by advice, information and personal assistance. A number of reports of progress and other presentations of parts of the work have been made at meetings of the Academy from time to time. An outline of the proposed survey was presented by members of the Com- mittee in the form of a symposium at the meeting of April 13, 1914.74 Another symposium was given at the meeting of December 14, 1914.7 At the meeting of the Section of Geology and Mineralogy on November 1, 1915, preliminary reports on field-work were given by Messrs. Semmes, Modge and Reeds.2* At the meeting of the Section of Biology Novem- ber 8, 1915, communications were presented by Messrs. Reeds, J. A. Allen and Matthew.?7 The Committee submitted a report of progress: at the annual meeting of December 20, 1915.28 At the meeting of the Academy held January 24, 1916, Dr. Boas, Mr. Aitken and Dr. Haeberlin” presented communications on ethnology and archeology, and at the meeting of May 15, 1916, geological communica- tions were presented by Messrs. Hodge, Semmes, Reeds, Fettke, Hub- bard,®° Lobeck and Professor Berkey.** During several months of 1917, Mr. Graham J. Mitchell prosecuted an areal geological survey of the southwestern portion of Porto Rico, and his report of this work is in progress of preparation for publication. Dr. Charles R. Fettke has recently published, with the approval of the Com- mittee, a paper entitled The Limonite Deposits of Mayaguez Mesa, Porto Rico.®? The final geological reports are being written, for the most part, by the 3 Bull. Am. Mus. Nat. Hist., XXXVII, pp. 183-189. ** Ann. N. Y. Acad. Sci., XXIV, pp. 369. * Ann, N. Y. Acad. Sci., XXIV, pp. 398, 399. 6 Ann. N, Y. Acad. Sci., XXVI, pp. 433-436. "7 Ann. N. Y. Acad. Sci., XXVI, pp. 436-439. *8 Ann, N. Y. Acad. Sci., XXVI, pp. 456-462. *7 Ann. N. Y. Acad. Sci., XXVII, pp. 250, 251. 29 Bull. Am. Inst. Mining Engineers, No. 135. 3 Ann. N. Y. Acad. Sci., XXVII, pp. 277-282. 22 Bull. Am, Inst. Mining Engineers, No. 135, pp. 661-676. 8 SOIENTIFIC SURVEY OF PORTO RICO several geologists who have participated in the field-work, and, as already stated, considerable portions of them are ready for publication. Dr. T. W. Vaughan, of the United States Geological Survey, has kindly con- sented to study the collections and prepare the descriptions of the fossil corals, and those obtained up to the present time have already been sent to him. The final botanical reports are being prepared by the following investi- gators: Flowering Planis——Dr. N. L. Britton and Mr. Percy Wilson, the grasses by Professor A. S. Hitchcock. Ferns and Fern Allies-—Preliminary work by Miss Margaret Slosson. Mosses.—Mrs. N. L. Britton and Mr. R. 8. Williams. Hepatics.—Professor A. W. Evans. Lichens.—Professor Lincoln W. Riddle. Fungi.—Dr. W. A. Murrill, Dr. F. J. Seaver, Professor J. C. Arthur, Professor F. L. Stevens, Professor H. H. Whetzel, Dr. E. W. Olive, Dr. John A. Stevenson. Alge (marine).—Dr. Marshall A. Howe. Alge (fresh-water and aerial).—Professor N. Wille. No arrangement has yet been made for the study of Porto Rican diatoms. The zodlogical collections are being studied and final reports prepared as follows: Mammals—Mr. H. E. Anthony.** Birds—NMr. Alex. Wetmore has published an exhaustive report on the birds which may be taken as a basis for our document.** Reptiles—Preliminary work by Miss M. C. Dickerson. Amphibians Preliminary work by Miss M. C. Dickerson. Fishes.—Mr. J.T. Nichols and Professor C. F. Silvester. Insects: Orthoptera——Mr. J. A. G. Rehn and Mr. Morgan Hebbard. Coleoptera.—Mr. C. W. Leng and Mr. A. J. Mutchler. Hemiptera.—Mr. H. G. Barber. Lepidoptera.—Mr. F. E. Watson. Hymenoptera.—Mr. J. Bequaert and Dr. F. E. Lutz. Myriopods.—Mr. Roy W. Miner. 33 Mem. Am. Mus. Nat. Hist., N. S., II, Part 2. % Bull. U. S. Dept. Agric., 1916, No. 326, p. 140. BRITTON, HISTORY OF THE SURVEY 9 Mollusks.—Preliminary work by Dr. L. P. Gratacap. -Ascidians.—Dr. Willard Van Name. Crustaceans.—Mr. Roy W. Miner and Dr. Willard Van Name. Anneltdes.—Professor A. E. Treadwell. E'chinoderms.—Preliminary work by Mr. D. M. Fisk. Bryozoans.—Dr. R. C. Osburn. Coelenterates—Mr. Roy W. Miner. Representative collections of Porto Riean protozoans have not yet been made. The anthropological and archeological documents are being written by the several investigators who have conducted the field-work. Pre- liminary papers, in addition to those already noted in this report, are being prepared by Professor Boas on anthropometrical observations in Porto Rico, by Dr. Mason on the archeological investigation of the very important site at Capa, by Dr. Aitken on the cave sites near Utuado, and hy Dr. Mason and Professor Espinosa on Porto Rican folk tales. As to the general progress of the survey, it may be stated that over two-thirds of the necessary geological field-work has been completed. Except for an investigation of the diatoms, which has not yet been ar- ranged for, no additional botanical field-work is really essential, although the final reports would be more complete if additional collections were made, but this is of course true all over the world. Considerable addi- tional zodlogical field-work and additional collections in several of the groups of animals are highly desirable, and, as before remarked, the pro- tozoa have not been collected. Anthropology and archeology still offer widely attractive fields for further examination. No oceanographic work has as yet been possible. , In cooperation with the Insular Government, portions of the collec- tions made have been returned to Porto Rico to form the basis of a Nat- ural History Museum, and other portions will be forwarded to Porto Rico as the study proceeds. The remainder is to be divided among the codper- ating institutions and investigators. The islands St. Thomas, St. Jan and St. Croix, recently purchased by the United States from Denmark, lie close to Porto Rico, to the east and southeast. It is highly desirable, before our survey is brought to a close, that these should be studied geologically, zodlogically and archeologically. Their botany is fairly well known. I have recently contributed a cata- logue of their known flora to the Brooklyn Botanic Garden, and this has been published in the volume of papers presented on the occasion of the 10 SCIENTIFIC SURVEY OF PORTO RICO opening of the new laboratories of that institution.*> The survey will thus be made to include all the Caribbean insular possessions of the United States as they stand at present, and be entitled A Scientific Sur- vey of Porto Rico and the Virgin Islands. The Chairman of the Committee gratefully acknowledges aid from the other members in the preparation of this historical sketch of the survey. 3% Mem. Brooklyn Bot. Gard., I, pp. 19-118. (Contributions from N. Y. Bot. Gard., No. 203.) INTRODUCTION TO THE GEOLOGY OF PORTO RICO By CuHarues P. BeERKEY CONTENTS Page Introductory statement... ...... cece cece eee eee eee eee e ee ee eens 11 Geological reconnaissance...... 62... cece ee eee eee eens eee nena 14 Major geological features... ... 0... cee ccc cece eee eee eee et cee e eens 15 Rock formations........... 0.0 ccc cee ee ee ee eet tenes rr 15 The Younger SerieS......... 2c. c ccc e cece cee cece tee eee e eae wee 16 The Older SerieS...... 0... ccc ccc eee eee eee nee eee eeees 17 Petrographic range... .. 0... cee ce cc eee ee ttn e ween eeeee 18 Structure... cc cece eee eee eee eee eee e tere tence tee eee 19 Relief features... ... cc cece ce ee eee eee ee eee eee teen ee wee eee eee 22 Geologic histOry.... 6... cece ee eee ee eee et teen ee ween eens 23 Problems of the Survey........ cece cc cee eee ee ee ee eee ee terete e eee eeee 24 Expeditions. ..... 0... cc cece cece cece cece eee eee tt eee n inne eeeeees 24 Classes of Studies... 0... cece cece eee cere rete e eet eet beeeeenees 25 General studieS........... cece cece tere rence ence ‘beet awe eneees 25 District studies, with outline map.......... ccc eee ee eee eens 26 Special investigationS......... 66. cece eee eee ee eet tee eee ee 27 DES Tt) 6 Koya a7) 9) | h ea 29 New base map of Porto Rico. By CHESTER A. REEDS..... sce te eee eeee 3U INTRODUCTORY STATEMENT The Island of Porto Rico lies between latitude 170° 54” and 18° 30’ north and longitude 65° 13’ and 67° 15’ west. It is the most eastern and southern of the Greater Antilles. Thus it lies within the trade-wind belt, which is an important factor in the local variations of its tropical climate. In the Atlantic immediately north of Porto Rico lies Brownson Deep, which reaches the profound depth of 24,000 feet, and in the Caribbean farther to the south lies Tanner Deep, reaching 15,000 feet. Although its loftiest mountains do not exceed 4000 feet elevation above the sea level, the whole island appears to be just a portion or segment of a great mountainous mass or chain that rises from a submerged platform above which its true relief might well be measured. A relief difference of 28,000 feet such as is given from the bottom of Brownson Deep to the (11) 12 SCIENTIFIC SURVEY OF PORTO RICO top of El] Yunque is not exceeded in many places the world over within such moderate distances, but it must not be assumed that this is the elevation above the submarine platform. Porto Rico may thus be regarded to some advantage in the present consideration as a badly eroded uppermost portion of a great mountain mass which probably at one time formed a part of a chain with general east-west trend, most of which is now submerged. Certain very elevated segments of this chain still stand above sea level and form the islands of the Greater Antilles. Whether or not the structural relations of these exposed segments are of fault-block type and what relation such an island as Porto Rico may have to a former continental mass extending toward and possibly connecting North and South America, however interesting or suggestive they may be, are questions that might be better discussed in the summary at the conclusion of this survey rather than in this pre- liminary statement. Such questions are involved in the final solution of the geologic history of the island, on which a whole projected series of district and special studies have a bearing. Porto Rico is very mountainous. A central cordillera extends nearly east and west, starting abruptly at the sea near Rincon on the west coast and continuing to El Yunque, the great mountain summit which forms the central feature of the eastern end of the island. It is not by any means as simple, however, as this statement would suggest, for there are branches of the main range both east and west, but especially to the east, where the Sierra de Luquillo, culminating in El Yunque, and the Sierra de Cayay, 10 miles farther south, form very distinct features. At either end of the island the chief mountain relief is centrally located, but throughout the whole of the middle portion and for two-thirds of the total length of the island, including the Sierra de Cayay, and thence westward for 60 miles, the chief mountain range lies only about 10 miles from the south coast. Almost two-thirds of the total area, therefore, belongs to the northerly slopes of the chief mountain range. Although the topography on the whole is very rugged and the island has a decidedly mountainous aspect, there is almost everywhere a very moderate relief along the coast and at many places the coastal lands are almost flat. These very flat areas lie always at the mouths of rivers and undoubtedly have been made in large part by deposition of the silts of the streams. Such alluvial tracts are called playas in Porto Rico. All relief forms except these playas are of erosional origin. Exceed- ingly steep slopes are the rule, suggesting early maturity in physiographic history. This phase of the geologic history of Porto Rico has been made the subject of a special study by Mr. Armin K. Lobeck and will soon be BERKLEY, INTRODUCTION TO THE GEOLOGY 13 published in this series. One of the most surprising things is the way the soils cling to these steep hillsides, and it is possible to repeatedly see slopes under cultivation that measure from 30 to 40 degrees. Numerous small islands lie along the coast. T'wo of comparatively large size, Vieques and Culebra, which are respectively 20 and 7 miles in length, mark the continuation of the Porto Rican land mass toward the east. All are included as a part of the studies of Porto Rico. Streams are numerous and surprisingly large. Mr. H. M. Wilson (1899, 1900) has published an excellent account of the hydrology of the island, and to this reference should be made for details of this nature. He credits this small island with 39 large and 1300 small streams. Rainfall is very unevenly distributed. At the east end, near El Yunque, there is an annual rainfall of 123 inches. On the other hand, at Cabo Rojo, at the extreme southwest corner, there is seldom any rain at all. Because of the high mountain ranges, there is an abundance of rain on the windward side, which includes the east end and most of the north side of the island, and since the principal range stands far south of the middle, the larger portion of the island is fairly well watered. A com- paratively narrow strip along the south side, especially to the west from Guayama, and again a strip at the northwest corner, are comparatively arid. Extensive irrigation works have been constructed along the south side. In most districts the bed rock is compact enough to discourage under- ground circulation and the run-off is correspondingly responsive to rain- fall. But in the northwest corner of the island, on a broad limestone belt reaching from Aguadilla to Camuy, and less prominently even farther eastward, there are many caves and sinks, and a most remarkable minor topography,’ where underground water circulation is locally of much importance. In some cases large streams rising on other ground farther inland are completely lost here for long distances, following subterranean channels in these limestones. There are no inland lakes and but few coastal Jakes. All of these appear to be related either to playa development or to comparatively recent elevation and subsidence. One near Guanica still retains internal evidences of its former marine relations. The climate is strictly tropical, but it is so tempered by reason of the trade-wind breezes and by the mountainous aspect and elevation of much of the country that it is usually very agreeable indeed. The entire lack of great changes of temperature and the prevailingly moist conditions 1¥or discussion of this feature in much more detail, see the following article by Douglas R. Semmes on The Geology of the San Juan District, Porto Rico. 14 SCIENTIFIC SURVEY OF PORTO RICO over most of the island have a direct influence on the character of rock decay and disintegration and also on the quality of the soil. The average daily temperature is 80 degrees, and it rarely rises above 90 or drops below 70, while the maximum is said to be 99 degrees. In area Porto Rico covers 3,670 square miles, and is therefore about three-fourths the size of the State of Connecticut. It is roughly rectan- gular in outline, with the longer axis cast and west, and in actual dimen- sions is approximately 35 miles in average width and 105 miles long. It is the fourth in size of the West India Islands. Porto Rico is very productive and is said to be the most densely populated country in the world. GEOLOGICAL RECONNAISSANCE The Island of Porto Rico has never had a systematic survey, and com- paratively few articles have been written on its geology. A few papers, however, have described certain special features and general physical con- ditions in a very instructive way. The writings of R. T. Hill (1898, 1899), especially, contain a comprehensive outline of the geologic history of the Island of Porto Rico, and those of H. M. Wilson (1899, 1900) and W. Dinwiddie (1899) give as good general description of its physical features as is anywhere to be found. In the summer of 1914 the writer, in company with Dr. Clarence N. Fenner of the Geophysical Laboratory, Washington, made a geological reconnaissance of the island, with the object of determining the chief lines of its geologic history and outlining the major problems to receive further study. This reconnaissance was undertaken as a part of the Natural History Survey planned by the New York Academy of Sciences and was intended to lay the foundations of a complete geological survey which it was expected would become the work of several subsequent expeditions and might extend over 4 or 5 years. Observations made at that time, together with additional studies of material secured on this first expedition, served as the basis of a report entitled Geological Recon- naissance of Porto Rico (Berkey, 1915), which was published the fol- lowing year, and has been the guide for several special expeditions and district studies since that time. This paper still constitutes the fullest statement of the structure and origin and geological history of the whole island ; but it has now been supplemented by several district studies which have been made in much greater local detail, and also by a special investi- gation of the physiography of the island; all of which, with yet others to be made, form a part of the plan for this Survey.? Seven such districts 2A detailed list of these topics and studies is given at the end of this article. BERKEY, INTRODUCTION TO THE GROLOGY 15 and areal studies and four general investigations were originally planned. Five of the district or areal studies have been made and one general investigation has been completed. MAJOR GEOLOGIC FEATURES | Determination of the principal rock types and larger structural units, together with their relations and the principal problems deserving fur- ther investigation, may be considered the chief work of a general geologic reconnaissance: ‘To this task the energies of the first expedition was directed with sufficient success, as it now appears with respect to its major lines, to stand the test of the more detailed subsequent work. A brief outline of the more important geologic features characterizing the whole island follows. Rock For marions There is an exceedingly large number of formational rock units in this field and a very great number also of rock types or varicties, and the confusion as a consequence is so great, at first sight, that it all appears a hopeless muddle. This is especially true of the interior of the Island rather than the coastal margins. In the higher interior regions igneous rocks and elastics derived more or less directly from igneous action such as tuffs and ashes prevail, although formations of simpler sedimentary (water laid) habit are very abundant and sedimentation structures are at least as prominent as are the massive structures of the true igneous rocks, Along the coastal margin, on the other hand, especially along the north coast west of San Juan and along the south coast west of Juana Diaz, the rock formations are much simpler in aspect. Soon one comes to realize, therefore, that two distinct formational series are represented and, judg- ing from the very marked differences in habit, one would expect them to he separated by a more or less profound break or unconformity. To this extent at least the first suggestion in an attempt to organize the complex structure of the island is correct. There are undoubtedly two very distinet formational series which, on more extended inspection, prove to be readily distinguished and separated. The one referred to as characterizing the interior is much the more complex in make-up and structure and most of its members have been extensively deformed and modified since their deposition. The simpler series is made up of a suc- cession of sedimentary and organic accumulations, including shales, marls, chalks and limestones, little disturbed. As should be expected, 16 SCIENTIFIC SURVEY OF PORTO RICO there is a very distinct unconformity between these two major series represented by an erosion plane which bevels the upturned members of the older complex and seems to have all of the earmarks of a peneplain. The complexity of the older of these two series suggests again the possi- bility of a subdivision of it, but all studies so far have failed to show a major line of separation. The formational groupings are therefore in approximately the order suggested in their original reconnaissance, essen- tially as follows: THE YOUNGER SERIES This includes shale and limestone beds, reef limestones and occasional sandstone and pebble accumulations. These are readily recognized as belonging to the Tertiary period, but the greater detail of age relation is a matter necessarily left for the more elaborate studies of those districts where these formations are prominent or to the results of general strati- graphic and paleontologic study. The Younger Series as used in these studies includes at least two very readily differentiated but very unevenly developed members which were referred to in the reconnaissance under names taken from their most typical occurrence. (a) The San Juan Formation is the most recent consolidated repre- sentative in the island. It is confined to the immediate coast margins, especially the north coast, and the adjacent small islands, the most strik- ing occurrence forming the promontory on which the city of San Juan is built. (b) The Arectbo Formation is a thick series of limestones, marls and shales. This is a much more extensive and geologically important mem- ber than the San Juan. Subdivision is doubtless possible with further study, and it has been convenient from the very first to distinguish cer- tain particular facies or the beds of particular localities by special locality names; but these do not necessarily represent subdivisions of wide appli- eability. They have been, however, of distinct usefulness in all studies thus far made. The most commonly used are the following: 1. The Arecibo limestone upper limestone member on the north side of the island. 2. The San Sebastian shales lower, shale member on the north side of the island. 3. The Juana Diaz marls south side shales and marls near Juana Diaz. 4+. The Ponce Chalk beds very white chalks near Ponce on south side of the island. BERKLEY, INTRODUCTION TO THE GEOLOGY 17 The greater part of all these beds are satisfactorily determined to be of Oligocene age, but the latest studies indicate the presence of representa- tives of both Eocene and Miocene age as well. THE OLDER SERTES This includes a complex association of tuffs, ashes, shale, conglomerate, limestones and a very great variety of intrusives and occasional lava flows. These are readily seen to be enough older than the other series to have suffered much additional modification of petrographic character and deformation, and it is comparatively simple also to determine that the members of the series as far as they bear fossil evidence seem to be con- fined to late Mesozoic age, perhaps wholly to the Cretaceous period. The Older Series thus far has failed to show even as distinct lines of subdivision as the Younger. Perhaps there are breaks as great as that between the San Juan and the Arecibo formations of the Younger Se- ries, but the structures are much more obscure, by reason of deformation and other changes, and are less fully exposed. There is a suggestion of a possible structural break marked by one belt of limestones found by Dr. Semmes in the San Juan district (see San Juan District geologic map) and perhaps in the La Muda Limestone of the original reconnais- sance account, but no other supporting evidence is vet at hand, even after a study of more than half of the island in detail. The Older Series is apparently a fairly continuous accumulation of no greater complexity and structural difficulty than should be expected from a long and almost continuous volcanic history. Although still regarded as a single series of formations, it has been found very convenient in this case also to designate certain well marked units by locality names. No assumption is made as to their extent or the possibility deserving recognition in attempts at correlation. The Recon- haissance expedition made free use of such terms to much advantage in , the field, and later still others have been used by the investigators of special districts. As a matter of fact, the great difficulty found in the beginning in following any single field unit very far or identifying it at other places made the use of many locality and arbitrary names particu- larly serviceable at that time. Subsequent studies have not successfully climinated them, and it may well be that the accumulating proof of the ereat variability of all these formations as well as other units will compel the retention of such local names. Among the terms that belong to the reconnaissance stage and that bid fair to be retained are the following : 18 SCIENTIFIC SURVEY OF PORTO RICO 1. The Fajardo shales, a very widespread type of blocky shale. 2. The Mayaguez shales, similar to Fajardo shales in general struc- tural habit. 3. The Coamo Tuff-Limestone, a heavy limestone carrving abundant tuff fragments. 4. The Trujillo Alta Limestone, a very limited occurrence of dense limestone. 5. The “Shred” Limestone, a name suggested by the appearance of the chief fossil form. 6. The La Muda Limestone, a formation that seems to mark a break of more than average consequence. i. The Mountain Limestone, of Hill—thin-bedded, shaly limestones and limy shales of very extensive development along some of the mountain ridges. & The Corozal Limestone, a peculiar local oceurrence of limestone breccia at Corozal. PETROGRAPHIC RANGE The petrographic variety of this older series is very great, but the types of large consequence are not numerous. They may nearly all be included within such group terms as limestone, marls, shales, sandstones, conglom- erates, tuffs, ashy tuffs, ashes, and ash shales among the organic sedimen- tary, and clastic rocks; andesites, andesitic porphyries, diorite, syenite and granite as the chief crystalline igneous rocks; and serpentines and gravwackes and rarely some contact products as the chief badly modified types. Although the range of different types when stated in this form is not at all remarkable, there is almost every conceivable variation of minor composition, quality, structural or textural peculiarity, physical condi- tion, degree of modification and state of preservation represented in each one. Most of them, furthermore, occur in an almost countless succession of beds and sills or other field units of all sizes from masses of many square miles in areal extent or hundreds of feet in thickness to thin layers or stringers or dikes of only a few inches. As a matter of fact, the most striking thing about these occurrences is the exceedingly great number of small units which alternate or change so many times in short distances that detailed mapping of them, or even an attempt to represent this detail by the most carefully constructed geologic cross-sections, seems hopeless. All practicable representations of the geologic structure are necessarily generalizations, BERKEY, INTRODUCTION TO THE GEOLOGY 19 Maps of any kind covering portions of districts must be done on the basis of a grouping together of great numbers of individual units in rec- ognition of the domination of some particular type. Thus it scems to be possible to mark out belts or areas of dominant limestones, shales, tuffs or conglomerates, some of which are fairly satisfactory as a basis for a geological map. But even in some of these cases the smaller individual constituent units vary so rapidly along their strike that the average quality is wholly different within distances of a few miles. This char- acter makes detailed geologic mapping a difficult and most discouraging undertaking. The Younger Series, on the other hand, is very much simpler, since no igneous rocks are represented at all. But even here, within the limits set by the shales and sands of one extreme and the marls, chalks, reefs and massive limestones at the other, there is every gradation, the character being evidently under the control of such local conditions, and so poorly marked off in succession by fundamental differences, that here again a subdivision for mapping purposes is extremely difficult to apply. A strictly paleontologic subdivision, however, is being more successfully applied as the investigation of certain districts proceeds. STRUCTURE The general geologic structure of the Younger Series of formations is simple. The beds lie, for the most part, dipping gently toward the sea. This is especially true of the broad belt of these rocks forming the north side of the island. On the south side there is some deformation, chiefly due to faulting and crowding. In many places also there is slumping due to sink-hole development. The Older Series has, on the contrary, a very complex structure. Only rarely do the bedded rocks have their original attitude. They commonly stand much tilted and even vertical, or in rare cases overturned, and faulting is common. But the most prominent structural feature is the association literally of multitudes of thin-bedded ashy or limy shales and equally thin igneous intrusive sheets or sills. It is not at all rare to see an alternating series of such units, a few inches or a few feet thick, so regular that when well weathered the whole succession looks simply like a series of alternating shaly and more massive beds. The number and complexity of the igneous intrusions are surprisingly great and at many places the intrusive members dominate in the formation. In most cases there are no noticeable contact effects. Much larger intrusive sills, which are almost always dioritic in com- position, are also very common and there are a few large bosses several 20) NCIENTIFIC SURVEY OF PORTO RICO miles across of granite, syenite and serpentine. hia few places the Jocal interruption of the he by massive taffs cut by intrusive complexes seems to mark old volcanic vents which must have heen active after the adjacent strata had formed and perhaps bad attained something of the quality and attitude that they new have. One large old vent of this kind is now the site of the Ja mas Reservoir, Phe occurrence of beds of limestone breccia. including great amounts of full fragments. and a continuation of the same regular beds bevond such complexes. are further supports to this interpretation, Big. 1. Diarite porphuny silts These sills are intruded between Jayers of near Comerio, The st calcareous shales and ash beds on the road ked or banded [i at the Jeft side of the print, are sills, A two layers at the extreme left. ers a shales, the massive portions, seen best fransgressive relation can be seen between the Minor structural features such as xenolithic inclusions in the intrustives are extensively developed. Sometimes a sill or dike is literally crowded with tall fy ements so closely packed together that the whole has more the general outward appearance of a tut! than a bona fide intrusive. Re- peated: inspection of the structure. however. has removed every doubt as to the essential correctness of the observation. A0 rather minor structure in the San Juan formation. which remarkable is believed to bea consolidated dune sand. ts illustrated in the accompanying figure. Tt BERNE), INTRODECTION VO THE GEOLOGY ra re Fe ae # oe i oe 3 sie ee ang ee sat ye oat a be die a ws si J: se ste fe 0a Fo Se we ae, ca = oo 0 O® a Ps 5 if bas nig tran nie sh 7 aby hae ms teh gy ate La hy vas sage Es <; ie i ey <# sy gir + Pg Dae a tig ie =. ee ea ., oe “ie aie ae oh, oe be? bs Se fPgé ok, Co iy ts oo comes Me; se Pes Aho jae aw ors ore fia pi ne Yaa - a on. i e fed ates ie a We Se Gy = a ey sje: tak ieee a La sape) 2 a. = ve ae Pape a 3 Ss j BS ae x Fy, agg by & - “i os si Seige eh ve PS a + ie bts Sie 5 a3 Ay say | ar hy ay > a fe hon ‘Sal 8! a eS tga eat < SF. ay rr Beloit of the double strnetin in the San duan formation at Lreciby This photograph was taken to bring out the horizontal strnehure crossing tle inelined Tnyers, There is no doubt whatever that the dark layer of less consolidated sand in the lower third of the photograph is a primary bedding structave, bat the horizontal ma ¢ View ave believed to he of seeonda sssing the inclined layers in the upper part of the origin 22 SCIENTIFIC SURVEY OF PORTO RICO shows nearly horizontal bedding at the base. with highly inclined thin beds (eross-bed structure) above, on which ov in which a less pronounced horizontal structure is also preserved completely crossing the inclined Javers. This formation has not been defommed at all, so the structures must be connected with the original sedimentation and perhaps the indu- ration processes in some way. No beiter explanation has been offered than that of the Reconnaissance report, which regards the cross-hed struc- ture as a wind-laid deposit and the horizontal structure, crossing it, as a cementation or induration structure developed in standing water during successive steps of subsidence and clevation. Big, 3. Haystack (nepine) hills A characteristic view, showing the small soil- hitls found in the re ered flats and moof the Arecibo formation, Photograph. tak nnd Barceloneta, sociated haystack n on the road be- tween Ared Rinne Pearcres The present relief features of Porto Rico are all those of simple erosion, In the interior the structure is so complex and variable that surface forms seem to show little structural control, ‘Uhe mountains are rugged, steep and irregular in outline. Mountain tops are almost everywhere kuife- edge divides. no matter whether they cross or follow the reck structure, The features of the coastal margins, however, are much more influ- enced by formational attitude. The younger series of beds lie on the rather evenly eroded (peneplained) sturface of the complex older series. Erosion has stripped back much of this vounger cover from the old land, BERKEY, INTRODUCTION TO THE GEOLOGY 23 thus developing the usual inner lowland and cuesta forms with traces of the old peneplain well preserved on the adjacent ground on the inner side. A full treatment of these features is included in a physiographic study of the island which has already been made by Mr. Armin K. Lobeck, and whose report will soon be published as a part of this Survey. On the cuesta and the outer slopes, wherever limestones are the surface rock, great numbers of caves have developed. A most striking surface feature is thus produced with sink-holes as the first distinct stage which. by enlargement develop flats separated one from the other by remnants of the old walls. In some districts these last remnants form great num- bers of small conical hills, referred to by Hill as the pepino hills and by Berkey as haystack hills. This is the most unusual and remarkable of the surface features of the island. Immediately along the coast one may find occasional traces of a step- like form which has attracted much attention. They were taken at once to be sea terraces, and subsequent studies seem to confirm that conclusion. Such forms, therefore, indicate that the island has been elevated in com- paratively recent time. Other related features, among them the occur- rence of marginal islands, suggest that at one time the island may have stood even higher than now. Probably there has been a succession of elevations and subsidences in later as well as in the earlier geologic history of the island. GroLtocic History In barest outline the geologic history of Porto Rico is simple. A com- plete or even a reasonably full account of the geologic history of Porto Rico cannot be written at this step of the investigation. , There is no record of very ancient rocks at all. But in Cretaceous time, or perhaps immediately before, this region was the scene of violent and long-continued explosive volcanic activity which resulted through many vicissitudes in the accumulation of thousands of feet of volcanic clastic matters, partly in massive unassorted condition, partly worn, transported and assorted, partly mixed with weathered detrital matters and organic growths, all together forming a great succession of tuffs, ashes, shales and limy rocks. The summary of the major historical items formulated in the original Reconnaissance report is still serviceable : (1) A long geologic period of volcanic activity, accompanied by mar- ginal attempts at assorting of fragmental and detrital material and organic accumulation disturbed from time to time by renewed or extended igneous activity. 24 SCIENTIFIC SURVEY OF PORTO RICO (2) A dying out of voleanic energy, greater stability of the mass with respect to elevation and subsidence, and erosional attack continued long enough to result in extended planation and partial baseleveling with final extensive submergence. (3) The development of an unconformable overlying series of shales, reef limestones and related deposits chiefly of organic origin, brought to an end by final re-emergence. (+) The development of present surface features under stream erosion and marine marginal attack, with modifications arising from oscillation of level. PROBLEMS OF THE SURVEY The problems that were suggested in the Reconnaissance report have eugaged the endeavors of several expeditions. Altogether seven have been made and four studies have been completed. Others are yet to be made. The whole plan with its accomplishments may be listed as follows: EXPEDITIONS (a) Expedition of 1914 to make a reconnaissance. 1. Dr. Charles P. Berkey and Dr. Clarence N. Fenner. Reconnais- sance report (Berkey, 1915). (b) Expeditions of 1915. 2. Dr. Chester A. Reeds. Study of Tertiary stratigraphy, and espe- cially an attempt to establish the subdivisions of the Younger Series and make paleontologic collections. New base map pre- pared (published with this paper). 3. Mr. Douglas R. Semmes. Study of the San Juan District (Semmes, 1919). 4. Mr. Edwin T. Hodge. The Coamo-Guayama District? (c) Expeditions of 1916. 5. Mr. Bela Hubbard. The Aguadilla-Lares District.+ 6. Dr. Charles R. Fettke. The Humacao District.4 7. Mr. Armin K. Lobeck. A general study of the physiographic his- tory of the island? (d) Expedition of 1917. 8. Mr. Graham John Mitchell. The Ponce District.‘ 8 Report ready for publication. 4 Report interrupted by the war. BERKEY, INTRODUCTION TO THE GEOLOGY 25 CLASSES OF STUDIES The whole list of studies of all kinds fall into three classes: (a) General studies, covering certain features affecting the whole island. (b) Areal or district studies, with accompanying geological maps. (c) Special investigations on problems suggested by local conditions or the material collected. GENERAL STUDIES Among the general questions which have been considered to belong to the island as a whole are the following: New Base Map—The making of an accurate detailed map, such as might be represented by topographic sheets of the kind prepared by the U.S. Geological Survey, is an undertaking much beyond the scope and facilities of this Survey. Hach investigator of a district has undertaken the correction of the maps available for his own area in enough detail for the purpose. These districts, however, are not complete to such a point that a general relief map for the island could yet be constructed from them. As a step, therefore, preliminary to that result, the data of all previously published maps, together with such notes as were available from field observation, have been compiled, under the direction of Dr. Chester A. Reeds, in the form of a new relief map which is published herewith. Physiography of Porto Rico.—After the reconnaissance and first dis- trict studies were made, it became apparent that a general physiographic study covering the whole island would be particularly desirable. The opportunity to make a complete study of an isolated land mass, with a physiographic history probably similar to most of the West Indian islands, seemed to be particularly good. Mr. Armin K. Lobeck under- took this study and his work is completed. Tertiary Stratigraphy.—This general problem, which was considered too broad for a district study, was recognized as a difficult investigation that deserved to be considered by itself. Dr. Chester A. Reeds entered upon the investigation by making a collecting expedition in the season of 1915. Tt was the intention to include in this study a determination of the principal subdivisions and boundaries of the Tertiary strata for the whole island, and it was hoped that this could be done on simple enough lines and promptly enough to be of service to all of the men doing district 26 SCIENTIFIC SURVEY OF PORTO RICO mapping and making local studies. The problem has been found espe- cially difficult and final results are not yet reached. In the meantime the practical matter of mapping has been solved in each district as well as may be, and probably no full statement of the Tertiary stratigraphy will now be attempted till all of these separate studies are available. Mineral Resources.—Considerable money has been spent in Porto Rico in mineral exploration. It is said that gold was secured in paying quan- tities by the Spaniards in the early days. One can see gold panning in a few places now. Many ores of other metals are also formed as well as other economic products. Almost none, however, have proven attractive as the basis of an industry, although much interest is attached to such possibilities. Mineral resources of sufficient value to establish these in- dustries are much to be desired, and it is one of the purposes of this Survey to make a final summary of all matters relating to this question in a general study after all of the districts have been fully investigated and reported. DISTRICT STUDIES, WITH OUTLINE MAP The basis of all detailed investigations is the district or areal study. It has been found possible to divide the island into areas, each of such size that it could be studied in sufficient detail for the purpose in a single season by one man. These districts are not necessarily of the same size or form. Their boundaries have been chosen, in part, in consideration of transportation facilities and field accommodation, and, in part, in con- sideration of the occurrence of special features deserving particular atten- tion or special study. It has been possible to assign to each investigator of a district of this kind some important problem of a fundamental sort in addition to his regular district mapping and description. On this basis the area of the whole island has been covered by seven districts. They vary considerably in size, depending upon the nature of the country and somewhat upon the complexity of the geological problem, and to some degree also on the amount of previous investigation in adjoining areas (sec outline map). The first two districts to be studied completed a broad belt entirely across the island from north to south, extending from San Juan to a point beyond Vega Baja along the north coast and from Guayama to a short distance beyond Santa Isabel along the south coast. This belt was chosen as a guide study and was intended to more firmly establish the major geological lines for further study of the rest of the island. The belt across the island was divided by a line from east to west in the vicinity of Barranquitas into a northerly and a southerly district. OUTLINE MAP. OF PORTO RICO SHOWING DISTRIBUTION OF DISTRICT STUDIES SAN JUAN ‘ 4, On Bx ee i yom =e. ict Ol SF bo : " o/, timed A eN yy muuch \ ado 1915 7] AY] eleetae © Berros WW; Comerio Bar: Ce ~ id PUces IM sarge Vorpe vem. itbonito at = ~~ ay Tiny (KCayey istric fX " ric Cpamo @ \ } Pevuelas Hod Ee ee (y mo Spring. Cee pm LA Salina: <a ee ) [Xe @ DERBERIA I. 7 5 MUERTOS I C Hosted by Google BERKEY, INTRODUCTION T0 THE GEOLOGY 20 Ran The northerly one has for convenience been designated the San Juan District from its principal city. A study of this district was completed by Mr. Douglas R. Semmes and the report on its geology, with geolovie map, forms a part of this bulletin. The south end of the belt, south of Barranquitas, was studied by Mr. K. T. Hodge. Ilis area has been commonly referred to as the Coamo- Guayama District. A special study of the nature and probable origin of the hot springs at Coamo has been included hy Mr. Hodge in his studies of this district. The Aguadilla-Lares District occupies the northwest corner of the island, extending southwest as far as Mayaguez. This was studied in 1916 by Mr. Bela Hubbard. he district includes the best material for a detailed investigation of the Tertiary stratigraphy. The Humacao District of the southeast corner of the island extends as far west as Guayama and as far north as Ceiba. This district contains one of the large areas of granite as well as the principal iron occurrence. The geology of this distriet was studied by Dr. Fettke in 1916. Tt in- volves these special discussions in addition to the district geology. The Ponce District of the south and southwest quarter of the island extends from a few miles east of Juana Diaz to the west coast and from the south margin to Mayaguez. This was studied by Mr. Mitchell in 1917 and was made to include the special problem of elevation and sub- sidence as marked by terraces, and also the problem of faulting. Two other districts are still to be studied. One lies in the northeast corner, occupying the area north of the Tumacao District, and may be called the Fajardo District. The other lies west of the San Juan District, extending to the vicinity of Camuy on the west and Adjuntas and the mountain divide to the south, where it touches the Ponce District. This is known as the Arecibo District. The accompanying outline map indicates the location of these districts and gives the names of the men who have been responsible for their individual study (see outline map). SPECIAL INVESTIGATIONS Special scientific studies not already covered by the general investiga- tions of group (a) or included in the district studies of group (b) are chiefly concerned with pure science investigations connected with paleon- tology. Immense collections have been made and seem to be worthy of elaborate study. It is expected that they may ultimately form a volume on the paleontology of Porto Rico. A considerable list of special topics enumerated in the original Recon- 2s SCIENTIFIC SURVEY OF PORTO RICO naissance do not deserve so elaborate treatment as that suggested above, and indeed are quite logically cared for in the different district studies. Some of them have been mentioned tn that connection already. A\moug those considered as representatives of the class are the following: (4) Mapable subdivision of the Younger Series. (5) Mapable subdivision of the Older Series Complex. (c¢) Nature and origin of the San Juan formation. (7) Reef-butlding organisms. (7) Changes in character and composition of the igneous products at different stages in Porto Rico voleanic history. ({) Thermal springs. (y) Studies in magmatic differentiation in an isolated volcanic center. (h) Origin of the Tron Ores, ete., ete. An occasional special topic has been the basis of a separate paper (Fettke and Tubbard, 1918), and some of these have been or will be published separately in an effort to furnish useful information as promptly as possible. Th spite of the complexity and extent of the original undertaking, most of it has already been completed so far as relates to the general studies, district. descriptions and special problems. One season's field-work on the seale of that of 1915 or 1916 would complete such work, and it would then be possible to make a final geological map of the islid and to write the summary of its areal, structural and economic geology and its geo- logical history. A completion of it to that consummation may be regarded as the immediate object of these geological field) studies. The paleontologic studies, in so far-as they are necessary to the historical treatment and stratigraphy, are to be included in the geologic investigations. — Subse- quent studies of all kinds and to any extent may be based on the collec- tions. and additional investigations along paleontologie lines will then be included in a separate volume under paleontology. BERKEY, INTRODUCTION TO THE GEOLOGY 29 BIBLIOGRAPITY BeERKEY, CHARLES IT. 1915. Geological reconnaissance of Porto Rico. Ann. N.Y. Acad. Sei., XXVI, pp. 1-70. DINWIpDLE, W. 1899. Physical features of the island (Porto Rico), Harper's Weekly, XLII, p. 248. Ferrke, ©. R., and Husparp, B. 1918. The limonite deposits of Mayaguez Mesa. Porto Rico. Bull. Am. Inst. Min. Engin., No. 135. Hint, R. T. 1898.) Cuba and Porto Rico, with other ishinds of the West Indies. New York. 1899. Porto Rico. Nat. Geog. Mag., X. pp. 43-112. 1899a. The forest conditions of Porto Rico. Bull. No. 25, Div. Forestry, U. S. Dept. Agric. 1899b. The value of Vorto Rico. Forum, XXVIT, pp. 414-419. 1899¢e. The geology and physical geography of Jamaica. Bull. Mus. Comp. Zool., XXXTY. SEMMES, DovuGnLas R. 1919. The geology of the San Juan district, Porto Rico. Scient. Survey Porto Rico and Virgin Islands. N.Y. A. S.. 7. pt. 1. pp. 35-110. Wirtson, H. M. 1899. Water resources of Porto Rico. Water Supply Paper No. 82. UL 8. Geol. Survey. 1899a. The engineering development. of Porto Rico. Fngin, Mag... NVI, pp. 602-621. 1900. Porto Rieo; its topography and aspects. Jour. Am. Geog. Soc., XXNIT. pp. 220-238. a0 SCIENTIFIC SURVEY OF PORTO RICO NEW BASE MAP OF PORTO RICO By Creesrer A. Reeps Following a short fossil-collecting season in Porto Rico in June and July. 1915, for the New York Academy of Sciences and the Porto Rican Government, the American Museum of Natural Tlistory cooperating, it seemed desirable for plotting results that a small outline map of Porto tico should be prepared. During October, 1915, such a map was drawn at The American Museum of Natural History by Mr. A. Briesemeister under my direction. Most of the data for the base sheet was obtained from a Jarge map which had been prepared by the engineers of the Interior Department of the Porto Rican Government. The four-sheet edition of the U.S. Coast and Geodetic Survey and the U. S. Post Route map of Porto Rico were also used. Before the end of October a solio print edition of one hundred copics of this new base map of Porto Rico was published by The American Museum of Natural History. Com- plimentary copies of the preliminary edition were distributed to the members of the Porto Rican Committee of the New York Academy of Sciences, to certain officials of the Porto Rican Government, to the various field men sent out by the New York Academy of Sciences to Porto Rico and to other interested persons. During December, 1915, the 100, 500, 1000, 1500, 2000, 2500, 3000. 3500, 1000 and 4500 foot contour lines were drawn on a separate sheet for superposition on the base map of Porto Rico which had been prepared in October. Data for this topographic map of the island were taken from various sources, chiefly the U. S. Coast and Geodetic Survey maps, the profiles and sketches of the engineers of the Porto Rican Highways Com- mission, the contour map of a portion of the south side of the island prepared by the Irrigation Service, the U. 8. Geological Survey’s topo- graphic sheet of the Luquillo Forest Reservation, together with H. M. Wilson’s topographic map of Porto Rico, prepared for the U. 8. Water Supply and Irrigation Paper No. 32, 1899. Numerous photographs by Professors C. P. Berkey and H. HE. Crampton of the Porto Rican Com- mittee of the New York Academy of Sciences as well as a large number by myself were of considerable assistance in the preparation of the topo- eraphie sheet. Fifty solio print copies of this contour map were issued VotuMRE T, Part I — 65°30 20 10’ - eevee eee, — = a“ - NEW BASE MAP ee es Pa onN,, ~OF a - ra _ ‘PORTO. RICO” ee 18° E pd | come from the latest Government Sources —J 30’ Ne “By CHESTER A. REEDS and A. BRIESEMEISTER 7 1 October 1915 y ou. 1c) Ge “CULEBRA....IS ND mun T0-~~. "525 Cay Rediniten Lose nd 20 S NO G50 os Crosscay® fone? Mt,Résaca ulebrita I 41 AQ fo 8.W. Ca San ngo; ox a co) a) °° hh Ww toad SoS 10. Se Q Cvy, Bt —_ VIEQUE S “ESLAND 4l0" BEL BEX ea see 492 Mt.Jalobre ast Pt. Minéay heer y je Pt Pn a ao 100. ote od on — la ones ee i pe) wl ene eneet on a ae wee Nos ee - - Nos. weno! No 300° 0° ~ ——— ib SN pa | C) 00’ LEGEND Elevations in Feet. Depths in Fathoms 4 Three Fathoms and less, dotted Area mere Roads completed era ett me = om ext. Roads under Construction —=h tanner cance hoads to be constructed eon ee weet: ~~ Native Roads —___ n 65°30" 20 ive oe tego het as oo pane Wreerniek & eRe A WOMB EAN Don oes anoae MEER, . he, ney Lie Paty URE Bes a4. st ne mee oe te ti ‘4 " of in aa ot wy a be ceeameesnn cant ” oe bs a) cen ze sony .: re r noe a s Wem nie oe a bytes Fee Ys, awe 3 Me id ’ ore Spee Er on “ey wo4i iy Se o ne %¢ A ed aa gs na fo on ve stl aay? f, ts aan - “6 ty ve ph ra Pad on a * ¢ Ss iD nope ee | ve om a 0} Pa a Y ra “ ma AG BS S ye % oan t eo ts ry fats u w ek 8 EA ‘ vi ay Br Pe FG at “4 ae ay NGS ae 2] obey " ad we w ue Ps ~# ay zy ore oe wom ws - my te, ae an om « eae ee ae ah on "y ar " + d a ie ~ . th neta Seay ae a tates ser sas pees ae POE REN TO NII rh . “ ‘s sawn ee sae — naam Google RHEDS, NEW BASH MAP OF PORTO RICO 31 by the Museum and complimentary copies were distributed as had been done with the base map. Early in 1916 the 10, 100, 300, 500 and 1000 fathom lines were added to the base sheet of October, 1915. Areas less than three fathoms in depth were dotted. This information was compiled from the various Porto Rican charts of the U. 8. Coast and Geodetic Survey. This map should be of interest not only to the scientist and tourist but also to the million inhabitants of Porto Rico, for it is legible, convenient in size and contains a vast amount of information. Hosted by Google THE GEOLOGY OF THE SAN JUAN DISTRICT, PORTO RICO By Dovucias R. SemuxEs CONTENTS SYNOPSIS. oe en ee ee eee eee eee eee eee etn eens Introduction... 6. ee ee ce ee eee eee tenet et eeeene Geographic Location... 0... cc ee ce eee ence cette eeeeee Natural History Survey of Porto Rico... 0... eee San Juan District... 0.0... cee ee te eee bee e ee eae Physiography of the Island... ... 0... eee eee cece ee cee eee ees Complex Mountainous Oldland... 0... ee ce cee nee e eee Peneplamation. . 0... ee ee ec nee cece cence enn tee eeeeae The Coastal Plain... 0. cee cc cece eee eee ne fete eee Mature Dissection... 00.0... ec eee cece cence eee tee ee eens Recent Submergence and Uplift..........0.0. 0.0000 e ce ee tee ee eee Physiography of the San Juan District.....0..0 000... cece ee ee eee ee The Dune Area... eee cee cc ee eee eee eee ene tt en etene Phe Playas... cc. ccc cece ee ee eee eee eee eee re ee eet tee eeeee The Tertiary Limestone Belt......0..0...0 00. ccc eee ee eet eees a cc The Inner Lowland... 0.0... 0... ccc eee cee cee ene t tet eeeee The Interior Mountainous Region... 02... 0.0.0. c ce eee cet et eens Incised Meanders.. 0.2.0.0... cece ec cee cee cee can tb eteees Stream Capture... .. 0... cece ec ee cee cece cece ee th eeeeeee Peneplane... cc. ce cece cee eee eee eee eens sg tt tetenes Rock Formations. 2.2.0... 0.0 ccc cece ccc cece cece eee e ce een gs thtteeens Playa Plains... 0... ccc eee cece nee thet ne eee Pleistocene (7) Deposits......... 0.0. cc cece cece cece e tet teeees San Juan Formation... 0.0.0.0... . 000 cc cee ence fete ees VPage 35 = L BEB AAS tr Lt alr Ltt stole ls 34 SCIENTIFIC SURVEY OF PORTO RICO Juan Ascencio Chert Beds... .. 2... ee eee eee cee teens Corozal Jasper Bed......... Lc eee eee eee eee eee eee eee teens Shales............. beeen e ee eee eee eet eeeeees voce erence SandstOnes..... cc ee cee cee ee ee eee ee eee eee ee teers Conglomerates... 00. ce ce ee eee nee ee ee tee eenee Tgneous Roeks.......... 2.00.0. 0 eee sce cece cece teenies dec e ee eee eeee Modes of Occurrence... 0.6. cc cee ee eee eee teen eee een eeeee Lavan... ccc ee ee ce ee eee eee eee eee eee eee eeeee SUIS. ce eee eee eee eee ee eee ete n oneness DIKOS. Cece ne eee eee ee eee nee ee tence ete Stocks and Bosses TOXtUT@ ce ce ce ee ee eee tent e eee cee scene Composition... 2.0... cee eee ee ee eee deen w eee ee eee eee Vitrophyts.. oc. cee ee cee ee ee ete eee e ene eeeee wees Rhyolites.. 0... ee cece ee eee eens seen ce cee eaees GYanites. 0. ee ce eee eee eee ee teen beeen eas Quartz Latites and Rhyo-andesites... 0.0... ce eee eee Quartz Monzonites... 0.0... ccc ee eee tenet eee ee ee Granodiorited. 0... ee eee eee eee eet tte see Dacites.. 0.0... cee eee eee eee sce ee eee eee tttee tees Quartz Diorites.......... we eee eee eee eee eee eee eee eens Trachytes. cc... eee eee te cee neces ee tenes wees Syenites.... 0.0.0.0... 000 cee eee eee sce eee ee wee ete eeeee .- TLatites (Trachy-andesites) oo... 0... cc cee ee eee tence eee Monzonites..... 00... eee eee ee eee sce e eee ee . ANde@SIt@S . 0 ce cece eee eee eeees see eee ee eee DiOVItES. Ce ence eee tence eee cteeeeeee Basalts. cee ee ee eee eee e et eet ee cree e aes Olivine Basalts... 0... ccc ee ee eee eee cece ce eeeeeees SUMMALY oe ee ee eee ee cee ee eee eee nee ee ceneeeens Structural Features... 0.0... ccc ec eee e nce c ence eeceneeeeee Unconformities. 2.0... 6c cc cee cece ee cee ec ene ene teeeeaeee Paulting.. 0. ce eee ee eee eet e ence eee ees teteeeees Volding. ccc cc cc cece ce eee eee eee e erence eeees Metamorphism..... 0... 00. cece cece eee cece eect e ee eeeeece Minor Structures......... see e ee eee eee Cross-bedding............. see ee eee ce ee eee e eee Solifluction................ see ences : Auriferous Quartz Mines........0 0.00. e eee eee Platinum... . 0... ce eee ee eee Copper... cece cece eee eens 66 67 69 TO 71 72 16 T6 m7 (bo 1 SHUMES, GEOLOGY OF THE SAN JUAN DISTRICT 35 Page 5st: 6 105 MaNZaNeSe..... ce cece cece eee eee cere eee eee renee ee ee ere eeeeee 105 Road Metal... 2.2.2... cece ee eee ee cece cette eee en ee eeeeee 105 Building Stone... ... cc. eee cece ete eee nee e eee eees 106 GUANO... cc cee ec cee ce ee eee ee eee eee e ene Teeeeeees 106 TllustrationS... 0... ccc eee eee eee eee eee eee eee nee e ete eenees 106 CroSS-S@CtiONS... 2 eee eee eee ee eee eee eee ete eee eens 106 PN C1 6 \< pa 106 Acknowledgments... 0.0... 0. cece ec eee ee eee eee eee ee eee eee ee eeee 107 Bibliography... ee ec cee eect e eee n ee cee eens 108 SYNOPSIS The area described in this report, which has been designated the San Juan district, lies on the northern side of the island of Porto Rico. It extends from the city of San Juan on the east to a point about two miles cast of Manati and southward as far as Barranquitas—an area roughly 500 square miles in extent. The San Juan district is a typical north- south section through the northern half of the island, the geologic and physiographic history of which may be regarded as essentially the same as that of the whole island. The physiographic history of the San Juan district is that of a complex mountainous oldland, which has been peneplaned, partially submerged, overlapped by a coastal plain, uplifted, maturely dissected, again slightly submerged and partially uplifted, erosion continuing in the interior from the time of first uplift. The formations of the district may be primarily divided into the younger series, or those that form the coastal plain, and the older series. or those that lie below it. The youngest formation consists of a coastal deposit of indurated lime dune sand of presumably Pleistocene age over- lving unconformably a limestone series, which forms the coastal plain proper. This limestone series, termed by Berkey the Arecibo formation, lies almost horizontal (dip 6° N.) and is now maturely dissected, giving rise to the typical pepino or haystack topography of the island. The Arecibo formation is regarded as upper Oligocene in age. In the north- western portion of the island, but not appearing in the San Juan district, ‘a lignitic shale member (the San Sebastian shale) which underlies the Arecibo formation. The age of this shale member is uncertain, but in all robability it is lower, Oligocene. The older series consists of marine and voleanic sediments with numer- 's intrusives. It is highly tilted and locally folded, resting uncon- 36 SCIENTIFIC SURVEY OF PORTO RICO formably below the younger series. ‘The sedimentary types represented are limestone, shales, sandstones, conglomerates, tuffs and ashes. With hardly an exception, these sediments are cither of voleanic origin or were deposited through volcanic processes, Even the limestones show bree- ciated structure and are, with few exceptions, merely accumulations of limestone fragments derived from older beds shattered by volcanic out- bursts. The foraminiferal content of certain shale and limestone beds in the upper part of the older series indicates that the beds are upper Cretaceous and Kocene in age. The lower part of the series is no doubt Comanchie. The peneplanation of the older series culminated along the coast before the deposition of the coastal plain, for the peneplane surface can now be traced underlying the Arecibo formation. Tn the interior, however, erosion continued until the uplift, which occurred in late Oligo- cene time, The older series is everywhere intruded by igneous rocks of many varieties. The predominant type is an andesitie porphyry. The tuffs and other sediments directly derived from voleanic sources are also of this general composition. The igneous rocks occur as extrusive sheets, sills, dikes, and small and moderate sized stock-like intrusives, The mineral resources of the district are not large. About 100 ounces of gold are panned annually from the rivers in the vicinity of Corozal. Gold quartz veins have been worked in the hills south of Corozal, but without success. In the barrio Pasto, southwest of Morovis, several copper prospects have been slightly explored. INTRODUCTION The Antilles and the Central American region have remained until the close of the nineteenth century almost a lerra incognila as regards their geological structure and history, Unfortunately, little study has sinee been devoted to this critical region which connects the two Americas, and until more accurate information regarding it is available our ideas of the geologic correlation of the two continents must remain largely conjec- tural. At the close of the Spanish-American war Porto Rico. being the closest. of our newly acquired imsular possessions, attracted a good deal of attention. During the first vears of the American oecupation much was written about the island and its inhabitants. Several very good papers describing its general configuration and geology were published during this period and a number of articles on particular features or the general aspects of the country appeared in current periodicals and in TDPorsey (1902), Hill (1899a), (1899¢), Wilson (1899), (1900). SUMMES, GHOLOGY OF THE SAN JUAN DISTRICT 3 -? proceedings of learned societies. Interest in Porto Rico, however, soon waned, and from 1902 to 1915 nothing regarding its geology was pub- lished. In 1915 a paper by C. P. Berkey appeared in the Annals of this Academy, which gives the first detailed and purely geological deseription of the island that has vet been written. GEOGRAPHIC LOCATION Porto Rico, the smallest and easternmost of the Greater Antilles, aver- aves 35 miles in width and 100 miles in Jength, presenting a regular rectangular outline three times as long as broad and alined nearly ex- actly east-west. Its shoreline is nearly straight and quite regular. The coast is usually low, with a few low promontories. The fringing keys and deep indentations characteristic of a more youthful stage in coastal development, and so abundantly developed on the Cuban coast, are en- tirely wanting. Its area is 3670 square miles, just 500 square miles less than the area of Jamaica, or about three times that of Rhode Island. Its population, considered as a whole, is the densest of any country on the elohe, Naturan Tisrory Survey or Porro Rico In 1904 an appropriation was made by the Insular Government of Porto Rico for the establishment of a Natural History Survey which was to be carried on in conjunetion with the New York Academy of Sciences. The geological phase of the survey was begun in 19tf when Dr. Berkey and Dr. Fenner spent a month on the island, making a geological recon- naissanee, preparatory to a subsequent and more detailed survey. The following year the writer was assigned to the San Juan district to begin this more detailed work. San JuAN Disrricr The region selected may best be called the San Juan district. as San Juan, the capital, is situated in the northeastern corner. The district is that area comprised between longitude 66° 05’ and 66° 27” west, and an east-west line through the town of Barranquitas about 21 miles south of the northern coast. The areal extent of the district is roughly 500 square niles, A corresponding area of similar width to the south was studied at the same time by Mar. EK. T. Hodge. In this way a belt 25 miles wide was surveyed entirely across a typical portion of the island. Three nonths were spent in the field, in which time a topographic map was constructed, the mineral resourees studied, and the geology plotted in as 38 SCIENTIFIC SURVEY OF PORTO RICO much detail as possible, considering the shortness of the time and the size of the area involved. THE PIPYSTOGRAPIEY OF THE PSLAND The general configuration and topography of the island have been well described by several writers. Dorsey (1902) has written an admirable description of the several types of topography one meets on crossing the island, with an especially detailed description of the limestone topography of the coastal plain. Wilson (1899) also has given a good general de- scription of the physical aspects, and Tall (1899) desertbed the physiog- raphy in connection with his geological reconnoissance of the island. The recent article by Berkey (1915) gives the most modern and detailed de- seription of the physiography and physiographic history of the island. The island of Porto Rico may be deseribed as a complex mountainous oldland, in the a! evele of development, which has been peneplaned, or reduced to an old stage of topographic development, submerged, over- lapped by a coastal plain, uplifted and maturely dissected, partially sub- merged, then re-uplifted and further dissected. ComMPLEX Mounratnous OLpLAND The most characteristic topographic feature of Porto Rico is its com- plex mountainous aspect. That portion of the island that rises above sea level is merely the eroded crest of a submerged mountain range of ereat complexity and magnitude. This eroded crest rises steeply from the sea to an average altitude of 2500 fect along the divide. Owing to difference in rainfall on the northern and southern side, the divide has been pushed to the south by the encroachment of the larger northern streams until it now stands two-thirds of the way toward the southern coast. The present position of the divide has also been accounted for by a theory of block faulting of the whole island with the front face of the block facing south (Berkey, 1915, p. 40). In the western portion of the island the divide is double, where it is parted by westerly flowing streams. Near Adjuntas the two divides join at the headwaters of the Anasco River to form a single ridge, which continues to Cavey, where it first swings southward, and then sharply to the northeastern corner of the island. The Luquille range forms another westward extending branch of the divide nearer the northern coast. The texture of the mountainous topography is medium to fine, excep for certain Jowland areas of coarser texture. The interior topography 1 SEUUMES, GEOLOGY OF THE SAN JUAN DISTRICT 39 predominantly the ridge or cuchilla type. The slopes are extraordinarily steep, slopes of 30-40 degrees being often seen. Between these ridges the streams run in V-shaped valleys. Some of the valley walls are very steep, but all variations from a canyon-like gorge to mature, open valleys are to be found. ‘The streams north of the divide are very numerous and of large volume, due to the abundant precipitation of the large per cent of run-off. Loisa, the Jargest river, rises only eight miles north of Arroyo Fig, 1.--Valley of the Plata, just below the power dam at K 19, Comerio Road Such steep yalley walls and boulder-strewn beds are characteristic of almost all of the mountain streams, on the southern coast. The Plata, next in size, rises the same distance north of Guayama. The larger streams rise high up in the mountains, and in the first few miles develop steep gradients characterized by falls, rapids and boulder-strewn beds (Fig. 1) ; then passing out into the lower coastal margins they acquire much more mature courses and_ finally swing in large meanders over the flat playa plains bordering the coast. Thus a typical stream such as the Plata on the northern coast may show every stage in development from youth to late maturity in its compara- tively short course to the sea. The complexity of this mountainous old- 40 SCIENTIFIC SURVEY OF PORTO RICO land is readily recognized from even the most cursory observation of its geologic structure. An endless variety of sediments and volcanics, steeply tilted and locally folded, are to be found intruded, permeated, and satu- rated by igneous rocks of many kinds, assuming an endless variety of forms. PENEPLANATION If one stands upon the summit of one of the central sierras and looks ‘out over the innumerable ridges that rise in all directions he may be im- pressed by the even crest line formed by the general accordance of sum- mits. This crest line apparently marks the present level of a peneplane the development of which began in Eocene and culminated in late Oligo- cene time. It is quite possible that the peneplane was never developed in any degree of perfection over the entire island. In some districts, how- ever, its present position is clearly defined, and near Mayaguez and Rincon undissected portions of this old upland surface can be seen. In this vicinity the level-topped areas are locally known as mesas. In other parts of the island no trace of an accordant skyline can be found. How- ever, a discordant skyline might well be developed in local areas through differential erosion or by subsequent warping. The evidences for and against peneplanation are discussed in more detail in another part of this report. The present elevation of the peneplane ranges from 2000 to 2200 feet near the divide to sea level along the coast. On the northern side it is partially covered by the younger coastal plain strata, but in the stream valleys it can be seen still preserved beneath the coastal plain. Elevations rising decidedly above its maximum elevation, such as El Yunke (3790 feet), Los Picachos (3700 feet), Ala de la Piedra (3650 feet) and Guilarte (3600 feet), must be regarded as monadnocks upon the peneplane surface. Tye Coastal PLAIN Overlapping the mountainous region, there extends for nearly the whole length of the northern coast a coastal plain of limestone and shaly beds, which reaches as far inland as Lares and to an elevation of 1200 feet. A similar coastal plain appears along the central portion of the southern coast. They are both of early Tertiary age, but whether they are exactly contemporaneous is uncertain. This fringing coastal plain varies in width from a mere line of isolated limestone hills, as seen south of San Juan, to a belt over ten miles broad north of Lares. On the southern coast it nowhere exceeds two or three miles in width. Overlying SEMMES, GEOLOGY OF THE SAN JUAN DISTRICT 41 the coastal plain on the northern side, and occurring as a string of fring- ing islands or low coastal promontories, is the San Juan lime sand. It is essentially an indurated dune sand composed of shell fragments and quartz grains. This sand extends nearly the whole length of the northern coast, except for the extreme eastern part, but it has not yet been reported upon the southern coast. Mature Dissecrion The coastal plain is characteristically mature in its stage of develop- ment. Some portions of it might be regarded as sub-mature, and towards the eastern end of the district, south of San Juan, dissection has con- tinued to late maturity. The larger area comprised between these two extremes, however, shows the rugged appearance of maximum dissection, characteristic of maturity. RecENT SUBMERGENCE AND Upuirr Since the deposition and uplift of the Tertiary coastal plain there is evidence of still later movement. The rock terraces described by Berkey (1915, p. 48) on the southern side of the island indicate that the sea was once at that level, while the presence upon them of recent shells fixes the time. On the northern coast recent marine shells are found some distance up the larger valleys at elevations of 100-200 feet. The subsequent uplift was not as great as the previous subsidence, for large areas of the San Juan sandstone, which must have originated at or above sea level, are now submerged, forming islands fringing the coast. The available evidence scems to indicate, moreover, a series of minor oscillations extending from Pleistocene time until the present, that is, the submergence which formed the fringing island was not continuous but consisted of numerous positive as well as negative movements. THE PHYSIOGRAPHY OF THE SAN JUAN DISTRICT The San Juan district, as already stated, extends from San Juan west- ward to a point two miles east of Manati and southward as far as Barran- quitas. Lying in the central part of the northern side of the island, it enjoys a very uniform humid climate. The mean annual rainfall varies from 50 to 90 inches. The dryest months are December and January, and the wettest month is May. The mean annual temperature varies from 74° to 78°. Though the climate is strictly tropical, the heat is rarely oppressive; a breeze is always stirring, and at least one or two showers may be expected each day. 42 SCIENTIFIC SURVEY OF PORTO RICO The district represents a typical section of the northern half of the island, and its physiographic history has in general been the same as that given for the island as a whole. The accompanving block diagram (PI. I) is an attempt to picture graphically the topography of the San Juan dis- ‘trict. Traversing the district from the coast to the southern boundary, one would cross successive belts of differing topography, which may be regarded as the topographic provinces of the district. On the coast is a narrow belt of modern sand dunes, in some places overlying the older Pleistocene consolidated sand dunes. Following this, there is an expanse of flat plains locally known as playas. These extend from the coastal dune area inland to the Tertiary limestones. In places the flat expanse of the playas is broken by low, rounded hills of the Tertiary limestones rising through it. To the south of the playa plains the typical pepino or haystack topography of the limestone belt begins. This belt extends inland and adjoins the oldland. It is occasionally broken by transverse valleys, such as the valleys of the Plata and Cibuco Rivers, which have completely removed all the limestone so that the alluvial plains of the river valleys rest directly on the oldland. Separating the coastal plain and the mountains proper is a low-lying area called by Hill (1899a) the “parting valley.” This is the inner lowland developed between the coastal plain cuesta and the oldland. It is well developed as it crosses the San Juan district, broadening out towards the east to form a lowland area several miles wide between Bayamon and Guaynabo. The moun- tainous area extends southward from the inner lowland to the southern boundary of the district. Tue Dune AREA The dune area presents topography of two types: first, the low promon- tories and coastal islands developed in the consolidated dune sand of Pleistocene (?) age; and, second, the modern dune topography that bor- ders the coast. The first type is best represented in San Juan City. The promontory, rising some 75 feet above the sea, on which the city stands, is entirely made up of the consolidated dune sand. To the west it can be traced either as a string of low islands, or occasionally as a promontory jutting out into the sea. Near Vega Baja Playa the island type is well developed, the islands ranging in size from a few vards to several hundred yards in length, and occurring out as far as a quarter of a mile from the coast (Fig. 2). The second or modern dune type of topography is a narrow strip of live dunes composed of lime sand similar in composition to that which forms the consolidated deposits. The dune belt follows the coast for the entire length of the district, varying in width from a few feet to several . : i ‘ " y y , \ , ‘A .) . Y \ Six N\ \ Y x \ SY ») yf i ) yy) RS Poy yi ) As? ie hye Son ES Hf Wh hy) :) "Y UV VY y 1 Qs hy fy 4A MEY 29)8 vy) yd S Xv N 8 *) Hosted by Google SEMMES, GEOLOGY OF THE SAN JUAN DISTRICT 43 hundred yards. It is broadest in the western part of the district, but its maximum width is developed farther west than the San Juan district extends. The origin and source of the Pleistocene, as well as the modern dune sand, will be discussed under a subsequent heading. Tire Phayas The playa plains, a name given by Hill to the fan-like plains that ex- tend from the foothills of the dissected limestone cuesta to the coast, are to be seen along the entire coast of the San Juan district. Separated from the sea by the dune belt, they extend inland to the ‘Tertiary lime- stones, and follow up the larger valley until they lie directly on the rocks Vig, 2.--San Juan consolidated dune sand forming fringing islands at Vega Baja Playa at the interior complex. The playa plains rise only a few fect above sez level, and until recent years large areas of the plains in the San Juan dis- trict have been covered with water, forming inland swamps and lagoons. Since the value of the land has been recognized for sugar-cane production, all the available areas have been drained, and now constitute the most productive and valuable lands on the island. The low, flat, monotonous expanse of the playa plains is occasionally broken by low, rounded hills of the Tertiary limestones rising above the alluvial (Pig. 3). These limestone hills are isolated remnants of the coastal plain here buried be- neath the recent deposits. Owing to the slight elevation that they afford above the blistering heat of the surrounding plains, they are selected as town and dwelling sites. Both Dorado and Toa Baja, the only two towns 44 SCIENTIFIC SURVEY OF PORTO RICO situated in the center of the playas, are built upon these limestone rem- nants. Others are chosen as sites for the individual dwellings of the natives. The playa plains follow the three principal valleys of the Cibuco, Plata, and Bayamon Rivers for some distance inland, and in the ease of the latter two extend well beyond the limestone belt. The geological history of the formation of the playa plains has, no doubt, been complex. It is evident that they are in part of fluvial origin, for they grade directly into the true alluvial plains of the river valley. Fic. 3. The playa pluins near Arecibo Showing a limestone remnant rising above the floodplain deposits and the limestone hills of the Arecibo formation in the background, Photographed from report of Bureau of Soils, U. S, Department of Agriculture, 1902. Just how important a rdle the sea has played in their formation is not definitely known. It is the writer’s opinion, however, that both factors have been influential. This point will be further discussed below. The rtrary LiesroNe BELT As the northern coast of Porto Rico is approached, one readily distin- guishes two kinds of topography; the rugged mountainous skyline, and the lowe inspection it is seen that the topography of the coastal plain consists of numerous isolated or closely grouped angular hills not exceeding 100 feet , angular, maturely dissected limestone coastal plain. On closer SEMME GEOLOGY OF THE SAN JUAN DISTRICT 45 in altitude, but of such angular and rugged outline, and so densely cov- ered with tropical vegetation that they form the most inaccessible and impassable regions of the district. Slopes of 40° are quite common and occasionally vertical faces of limestone rising 10 or 20 feet are to be seen, Though from a distance the hills appear well rounded, yet at close range they are exceedingly rough and jagged, and are, as one of the Americans living in the vicinity expressed it, “very hard to scramble up.” The unusual appearance of these limestone hills was early noticed by the na- topography as developed in the western portion of the San Juan District Photographed by H, EB. Crampton tives, who call them pepinos or cucumber-shaped hills. Berkey has used the term “haystack hills,” a term peculiarly fitted to picture their appear- ance, rising abruptly as they do from comparatively level plains (Fig. 4). Both Dorsey (1902, p. 800) and Berkey (1915, p. 5%) have independ- ently come to the same conclusion as to the origin of the haystack topog- raphy. Berkey summarized the steps in their development as follows: The reef limestones are not uniform in composition or structure. They have more or Jess intermixture of earthy matters which are distributed irregu- 46 SCIENTIFIC SURVEY OF PORTO RICO larly but chiefly at certain horizons, as more earthy or shaly beds of no very great lateral or vertical extent. Such conditions are repeated at occasional intervals in successive horizons. As such a series is lifted above sea level and subjected to ordinary erosion and weathering, the tendency is, (a) for the purer and more massive reef limestones to be attacked by the solvent action of percolating water with a development of underground channels, porous rock condition and actual caverns, (b) for the more earthy layers to resist and limit such action at the levels where this matter is present in sufficient abun- dance, with a development of residuary material. As this action progresses toward maturity, many of the larger caves collapse and sink-holes are thus formed. With still further development, the sink-holes merge into each other in local areas where solution has been most active, the earthy debris forms a soil in the bottom corresponding in level with the first important earthy layer, and adjacent remnants of the limestone reef stand out as sharp, rugged hills separated by irregular notches that represent other smaller, collapsed caves. The result of such action and conditions, finally, is the numerous ‘haystack’ hills standing on flat soil-covered areas or surrounding such areas as if they were just set down as bunches on the surface. This is no doubt the best explanation for the origin of the typical hay- stack hills. Towards the south boundary of the limestone belt, however, the haystack hills are not typically developed. The topography of this region is more rounded, with better drainage pattern. Occasional sink- holes are developed, but the topography as a whole resembles more that developed by normal stream erosion. This difference is due to the change in character of the limestone. The haystack type is developed on pure limestone, the latter on shaly limestone and shales. TERRACES The haystack hills rise abruptly from almost level plains, just as hay- stacks on a grass field. The plains are local developments and do not continue over extended areas. On passing from one of these plains to another, one is conscious of the fact that they rarely are of the same alti- tude, that is, they are not separated portions of a continuous base-level. On the contrary, they assume a step-like succession, forming a series of seaward-facing terraces. The level of an upper terrace corresponds roughly with the summits of the haystack hills on the next succeeding lower terrace. The terraces are best developed west of Vega Baja. Two can be recognized on following the road from Vega Baja to Morovis at K? 42-43 and K 3-4 (Morovis road) respectively (see topographic map). Others less prominent can be detected by means of the aneroid. There are two possible explanations for the origin of the terraces: “K indicates kilometer posts on the public roads. SEMMES, GEOLOGY OF THE SAN JUAN DISTRICT 47 (a) The presence of a shaly layer in the purer reef limestones may be the controlling factor in the development of a plain at a particular level through difference in solubility. The pure limestone would soon develop large caves, extending down to the level of the shaly layer, which, col- lapsing, would leave the haystack hills on a fairly level base. This plain would slope gently with the limestone strata towards the sea. After a time erosion would finally break through the shaly layer and a new ter- race would be formed with the next shaly layer as its base (Fig. 5). In this way successive terraces would be formed facing the sea. The differ- ence in appearance of the pure limestone and the shaly layers might well be so slight as to escape notice, so the apparent absence of shaly beds throughout the upper limestones would not disprove the theory. The writer located several shaly beds in the upper limestone that might easily have caused the terraces, but no exact correlation could be made from the barometric readings. (b) It is also possible that these may be marine terraces. Evidence for recent subsidence has already been mentioned, and marine terraces of Fic. 5.—Section through the Arecibo formation Illustrating the possible origin of terraces from differential solution caused by shaly layers at A, B and C. about the same elevation have been described from the southern coast (Berkey, 1915, p. 48). Both causes may have been influential, but the writer is inclined to adopt the first, since no marine shells have yet been found on the terraces. Moreover, the haystacks on the plains are more numerous and more promiscuously scattered than marine stacks should be, unless one considers the possibility of marine terraces later dissected to form the haystack hills. The limestone belt extends across the whole district. It is wedge-like in general outline, being about five miles wide on the western border of the district, and thinning to a mere string of isolated hills on the east. Its inner margin reaches the elevation of 700-800 feet north of Corozal. In this locality and to the west its southern boundary is a well-defined cuesta which is locally known as “The Walls” (Fig. 6). To the east of Corozal the cuesta form is destroyed by more advanced erosion. THE INNER LOWLAND This topographic province, described by Hill as the “parting valley” (Hill, 1899a, p. 105), extends entirely across the San Juan District. It 4s SCIENTIFIC SURVEY OF PORTO RICO lies between the infacing cuesta of the coastal plain on the northern and the mountainous region to the south. It is best defined at Corozal (Fig. 7) and to the west. Hastward it broadens as the limestone cuesta wedges out, until south of Bayamon it is represented by a broad expanse of rolling country, extending southward past Guaynabo and merging gradually into the interior mountain. Its topographic development is more than that of the interior mountains, that is, its stage of development is late maturity, with mature streams crossing it in broad and often meandering courses, TILE INTERIOR MOUNTALNOUS REGION South of the mner lowlands the topography of the San Juan District is typically mountainous. On approaching the island the rugged serrate lie. 6.-—Jnface of cuesta and inner lowland wear Corozal Showing relation of the Corozal limestone in the older series. character of the skyline can be distinguished soon after its outline rises above the horizon. Passing through the mountainous area one is tm- pressed with the extreme degree of the dissection. Almost no level ground is to be seen. Throughout most of the mountainous region of the San Juan District the country has attained the maximum ruggedness characteristic of a fully mature stage in topographic development. Other portions show more or less advanced stages, but the topography of the region as a whole is mature. Between the numerous streams the divides form a network of sharp ridges, so steep that the natives have appropri- ately named them cuchillas or knives. These are likewise closely and deeply corrugated by ravines and gullies, the whole region assuming very much the appearance of a wrinkled handkerchief, a simile said to have SEMMES, GEOLOGY OF THE SAN JUAN DISTRICT 49 been used by Columbus in describing the topography of the Antilles to Queen Isabella. The drainage of the mountainous area as a whole is dendritic in pat- tern. The adjustment of the stream courses to underground structure is very rare. A few cases were noted where some adjustment had taken place, but nowhere was it conspicuous. Although the mountainous region is underlain by a complex of formations of much variety, yet there is little or no evidence of this in the topography. Occasionally a dike could be traced for a short distance as a poorly discernible ridge, and it was no- FG, 7.--he inner lowland and the inface of the cuesta at Corozat ‘The almost vertical inface is locally known as ‘Lhe Walls.” Photographed by H. EB. Crampton, ticed that the highest points were usually underlain by highly indurated siliceous tuffs, as, for example, Torrecillo, northwest of Barranquitas, and felechal, some distance south of Bayamon. INCISED MEANDERS Some of the streams have developed deeply intrenched meanders as they pass out from the mountainous oldland. The best example is that 50 SCIENTIFIC SURVEY OF PORTO RICO of the Orocovis River south of Morovis. In this region the stream shows larger swinging meanders entrenched to the depth of 800-1000 feet (see topographic map). The origin of these incised meanders and their re- striction to the inner lowland and the adjoining mountainous region is comparatively simple. At the time peneplanation reached its maximum the streams passing out over the flat oldland surface acquired meandering courses on nearing the sea, which then reached inland as far as the present mountainous region. Subsequent gradual uplift has slowly entrenched these meanders as the coastal plain emerged and assumed the present position. STREAM CAPTURE Although there are undoubted cases of stream capture in other portions of the island, no striking examples are to be found in the San Juan dis- trict. Near Comerio, however, there is a wind gap that was evidently at one time occupied by a tributary of the Plata River. This tributary, now represented by Mora Creek, formerly flowed from the southeast through the wind gap and occupied the upper valley of the Arroyato River (see topographic map). Subsequently another tributary of the Plata, work- ing down from the north, intercepted the larger stream, forming the present Arroyato River, which joins the Plata at K 23 on the Comerio Road. Both streams are now completely readjusted, but it is still evident that Mora Creek occupies a much larger valley than would be expected, considering its volume. PENEPLANE It has already been stated that the interior mountainous region has been partially truncated by peneplanation. In the San Juan district practically nothing of the upland surface remains. In some portions, however, its present elevation is well marked by the even character of the crest line. In the southern part of the district it can be traced at an elevation of 2000-2200 feet or less towards the eastern corner. From this elevation it slopes to the edge of the mountainous region, where it is approximately 1200 feet. At this point the mountainous region breaks sharply down to the inner lowland, forming a well-defined escarpment. The escarpment can readily be traced on the topographic map, especially in the central portion of the district just north of Naranjito. The peneplane level, occasionally discernible among the crests south of the escarpment, is not again recognizable until it plunges below the lime- stone strata of the coastal plain. At Corozal its elevation as it passes “under the coastal plain is about 300 feet. From this it would appear that the peneplane surface was slightly upwarped along the southern edge of SHEMMES, GEOLOGY OF THE SAN JUAN DISTRICT 51 the coastal plain; but these irregularities in the present surface of the peneplane may well have been original. The peneplanation was by no means perfect. In some portions of the district no indications of its former existence are to be found. Between Barranquitas and Barros much of the country rises far above the peneplane level. Such an area can be regarded as a monadnock group. On the other hand, near Cidra, in the southeastern corner of the district, the general elevation of the country lies below the peneplane level. In this area the peneplane either was less uplifted originally or its original elevation has been entirely destroyed by subsequent erosion or warping. Indeed the present irregu- larities of the skyline and the variations in the general elevation of the upland surface are of such magnitude that the writer is forced to admit that the area may never have been peneplaned, and that the apparently even crestline that can be seen in parts of the district may be partly the _result of an optical delusion on the part of the observer, and in part a real evenness, not necessarily caused by peneplanation, but due to weather- ing in sitw and the formation of a thick soil mantle, which would tend to destroy the minor irregularities in the skyline. ROCK FORMATIONS The formational units of Porto Rico may be primarily divided into those that form the coastal plain and those that lie beneath it. These have been named the Younger and Older Series by Berkey. They are everywhere separated by a marked unconformity, so that they are entirely distinct structurally as well as lithologically and faunally. In the San Juan district the younger series includes all the formations encountered in passing from the coast to the inner lowland. These are, in the order of their respective ages, as follows: |. The modern sand dunes of the coast and the adjoining playa plains. . The Pleistocene (?) San Juan lime sand. . The Oligocene limestones and shaly limestones (Arecibo formation). . The San Sebastian shales, developed near Lares, but not in the San Juan district. Probably Upper Eocene or lower Oligocene in age. A detailed subdivision of the younger series will, no doubt, be possible when its fauna has been studied with care. The Arecibo formation is essentially a unit, though somewhat complex, and showing considerable variation laterally. The lower shale member is evidently a separate for- mational unit, merely representing a local development, which is not ‘ound in the San Juan district. A subdivision of the underlying older series, however, is.quite another matter. The complexity of the forma- — 2 © he 52 SCIENTIFIC SURVEY OF PORTO RICO tions and their lateral variations are so great that nothing more than a general subdivision will probably ever be possible. The local development of many of the formations, together with their disturbance and alteration by igneous agencies, make even the most generalized correlations largely conjectural. YOUNGER SERIES RECENT DEPOSITS Unconsolidated Lime Sand.—The modern dune sand, the occurrence of which as a narrow belt along the coast has been mentioned, consists of shell and coral fragments with occasional grains of quartz. Its constit- uents are almost identical with those of the associated consolidated de- posits—a fact which leads one to infer that this sand is but a modern representative of the older consolidated San Juan sand. The belt of modern sand dunes is usually narrow, its greatest elevation of 8-10 feet being reached within 75 yards of the coast; from this point it slopes gradually inland and merges into the adjoining playa plains. Playa Plains—The playa plains, which oceur as an east-west belt across the district, lying immediately south of the dune district, are partly fluvial and partly marine in origin. They are composed of ma- terial derived from the interior of the island through the ordinary proc- esses of stream erosion and deposited by the streams passing out of the mountainous interior upon the comparatively level coastal plain. These streams are now slightly entrenched, giving occasional exposures of a few feet in thickness. Such exposures show typical torrential bed- ding and deposits of fluvial character; however, marine shells are occa- sionally found upon the playas. These can be accounted for through temporary inundations. During the hurricane of August, 1898, practi- cally the entire expanse of the playa plains of the district was flooded. At this time the simultaneous occurrence of heavy rains and strong north- east gale caused the inundation. It is evident, moreover, that the sea has not had direct access to the plains since the consolidation of the San Juan sand. Indeed the formation of an offshore sand bar in Pleistocene time may have been the controlling factor in the formation of the playa plains. In the sheltered lagoons formed behind the bar the alluvial material may have been deposited and subsequently uplifted with the San Juan for- mation. This would account for the typical fluvial appearance of the deposits, as well as their occasional evidences of the action of marine agencies. Hosted by Google SHEMMES, GEOLOGY OF THE SAN JUAN DISTRICT 107 the plane-table and telescopic alidade, the contours being sketched in from aneroid readings. The main roads and streams are shown with some degree of accuracy, and a reasonably correct idea of the character of the topography can be had from the contours. When one attempts to map an area of 500 square miles of country as complex geologically and topographically as Porto Rico, in a single sum- mer, any great degree of accuracy is manifestly impossible. The sub- divisions of the older series are necessarily somewhat arbitrary, for the members of the series, as a rule, do not maintain sufficient constancy to make close subdivision possible. Many of the division boundaries shown on the map are generalized or are compromises because there is a con- tinuous gradation between some of the formations. Even the boundaries of the intrusives are obscure in much of the area. Some were located by single or widely separated exposures in districts of almost continuous soil cover. The dominant rock type is indicated, however, in each case and the approximate distribution and general trend and relative impor- tance of the larger formational units are brought out by the different color patterns. ACKNOWLEDGMENTS I am greatly indebted to the professors of the Department of Geology at Columbia University for their constant advice and valuable assistance in the preparation of this report; especially to Dr. C. P. Berkey for his field directions and assistance in making petrographical determinations, to Dr. D. W. Johnson for his advice and assistance in preparation of the manuscript, and to Dr. A. W. Grabau for his aid in the determination of many of the fossils collected. For the identification of other species I am indebted to Dr. Dall and Dr. Bagg, without whose assistance few of the conclusions as to the relative ages of the formations could have been derived. I appreciate, moreover, the advice and aid given me by the officials of the Government of Porto Rico, and desire to thank especially Judge Bonner, the Auditor; Colonel Shanton, the Chief of the Insular Police, and Mr. Bishop, the Assistant Auditor, for advice, assistance and support in organizing equipment and getting established in the field. Many others throughout the island, by their courtesy in giving infor- mation and their never-failing hospitality, did much to further the com- pletion of the work and make my visit to Porto Rico an enjoyable one, and, I hope, a serviceable one as well. 108 SCIENTIFIC SURVEY OF PORTO RICO BIBLIOGRAPHY Based upon the bibliography published by Berkey (1915). Additional articles have been added and the bibliography revised to date. ALEXANDER, W. A. 1902. Porto Rico—Its climate and resources. Bull. Am. Geog. Soc., XXXIV, p. 401. Brief notes on the natural resources, including mining, BERKEY, CHARLES P. 1915. Geological reconnoissance of Porto Rico. Ann. N. Y. Acad. Sci., XXVI, pp. 1-70. The most modern and detailed description of the geology and physical features of Porto Rico. CheEvE, TP. T. 1871. Geology of the northern West Indies. Kongl. Sevenska Vetenskaps- Akad. Handlingar, IX, No. 12. . With naps. 1883. Outline of the geology of the northeastern West India Islands. Ann. N. Y. Acad. Sci., II, pp. 185-192. Cretaceous age of the older series recognized. Crampton, H. E. 1916. Porto Rico. Am. Mus. Jour., XVI, Jan. DINWIDDIE, W. ; 1899. Physical features of the island (Puerto Rico). Harper’s Weekly, XLIII, March 11, p. 248. 1899a. The great caves of Puerto Rico. Harper’s Weekly, XLITI, March 25, p. 293. DoMENEcH, M. K. 1899. Mineral resources of Porto Rico. Mines and Minerals, XTX, pp. 529-532. , Dorsry. C. W. 1902. Soil survey from Arecibo to Ponce, Porto Rico. Report of Bureau of Soils, pp. 793-839. An accurate and comprehensive description of the topography and gen- eral configuration of the island. . Facconer, J. D. 1902. Evolution of the Antilles. Scot. Geog. Mag., XVIII, pp. 369-376. A brief geologic history of Central America and the West Indies. GANNETT, HENRY 1901. Gazetteer of Porto Rico. Bull. U. S. Geol. Survey, No. 183. Guppy, R. J. L. 1909. Geological connections of the Caribbean region. Trans. Canadian Inst., Jan.. pp. 873-391. SEMMES, GEOLOGY OF THE SAN JUAN DISTRICT 109 Fiske, Amos K. 1899. The West Indies. G. P. Putnam's Son, N. Y. Social and economic conditions. HAMILTON, S. HARBERT 1909. Note on some of the ore deposits of Porto Rico. Eng. and Min. Jour., LXXXVITI, Sept., p. 518. Hitt, Ropert T. 1898. Cuba and Porto Rico, with the other islands of the West Indies. New York. An illustrated book describing the islands and their inhabitants. 1899. The value of Porto Rico. Forum, XXVII, June, pp. 414-419. 1899a. Porto Rico.: Nat’l Geog. Mag., X, pp. 93-112. An excellent description of the topography and a brief résumé of the geology of the island. ° 1899b. The geology and physical geography of Jamaica. Bull. Mus. Comp. Zool., XXXIV. A detailed description of the geology of Jamaica. 1899c. The forest conditions of Porto Rico. Bull. U. S. Dept. of Agric., No. 25. A discussion of the forest conditions as well as the topography of the island. 1899d. Mineral resources of Porto Rico. Ann. Rept. U. 8S. Geol. Surv., XX, part VI. A résumé of the mineral resources and a short description of the most important occurrences. NEwpeRRY, J. 8S. 1882. Geology of the West Indies. Trans. N. Y. Acad. Sci., I, pp. 23-24. Nitze, H. C. B. 1899. Investigations of some mineral resources of Porto Rico. Ann. Rept. U. S. Geol. Surv., XX, part VI, pp. 779-878. Report U. S. WEATHER BureEAv, 1914. Porto Rico. SIEvERs, W. 1895. Zur Kentniss Puerto Ricos. Mittheil. Geogr. Ges. Hamburg, Heft. II, pp. 217-236, pl. 4. Spencer, J. W. 1904. The Windward Islands of the West Indies. Trans. Canadian Inst.. VII, pp. 351-371. 1908. On the geological relationship of the volcanoes of the West Indies. Victoria Inst. Jour. Trans., XXXV, pp. 189-207, 1 fig. General discussion of the relationship of the West Indies and the Wind. ward Islands to the Central and South American continents. VAUGHAN, T. W. 1902. Earliest Tertiary coral reefs in Antilles and United States. (Ab- stract.) Seience, XV, March 28, ve ie peasy a tas! apne ee te dae ak eae Te “ae ee oe Sant ae tate Lene ty ets fie My es to es st aoe a ei Tae ae AND THE: tie VIRGIN ISEANBS ee es ae we we er ~~ cy be f er = & Sf He 1k DY 3O le