MyM.'^' m m -M Q ip... iF^ii "- '11 ^:-^mm- 111 f.: :':•!:■ ■<:■ Mz^-iij;; ;" : i.^; » :;,■• '■: ;.;.:'■«■■■ :'.i ■.-. :.■■■•■•.. :.■• -j-- . ; :, ^ ^ : :., ■ ■'■• " ;■ ■; •■.:■■ : ■ :.iV ■ ■■. :. ■■ ■■■ ■ ■ ■...■■.:■■: ; ■: flr^tfiilP^ in I,' K N!:VV YOi^K ACADEMY Ol' SCIENCES SCIENTIFIC SURVEY OF Porto Rico and the Virgin Islands \C)I UME i CONTENTS OF VOLUME I rage Title-page i Contents iii Dates of Publication of Parts iil List of Illustrations iv Errata vii History of the Survey. By N. L. Britton 1 Introduction to the Geology of Porto Rico. By Charles P. Berkey 11 New Base Map of Porto Rico. By Chester A. Reeds 30 Geology of the San Juan District. By Douglas R. Semmes 38 Geology of the Coamo-Guayama District. By Edwin T. Hodge Ill Geology of the Ponce District. By Graham J. Mitchell 22J) The I*hysiography of Porto Rico. By Armin K. Lobeck 301 Index 3S1 Dates of Publication of Parts l»art 1, September 26, 1919. Part 2, May 25, 1920. Part 3, March 1, 1922. I*nrt 4, December 20, 1922. (iii) iJsT OF njj'STiiArioxs Pr.ATKS I.*:ige \. lU(K-k I Hn.irraiti (>{" tlu' Saii Juan I>istrir{. T. it 42 H. Fnnna of the AriM-iho Format }<»u .">s I [ r. Foninninficai haystaek topography as develoi>ed in the western portion of the San Juan District 45 SiH'tion through tlse Arecibo foi'niation 47 inface of cuesta and inner lowlanosed of tho San Juan consornhated lime san San Juan ecnsolidate4 i^xfoliation producing coTiceiitric arrangenuMUs in ash beds south (*f Ua\ amon <>2 ("runijding due to solitlu^> Tyfdcal foraminif^ Chart showing tlie ndative positions; of the pri!icii)jfi foraminifera I beds.. T*» Di<»rite porphyi*y sills intruded betW(M^n layers of sliales and ashes at K 20. ( 'omerio Road 77 Faulted] tracliyte dike crossing the f.a I'lata Ulver 7s l*hotomicrograi)h of \-itro})hyr (>ecurring north of (Mdra so lihyoHte porphyry sii Soda granite, slntwing poikiiitic struct vu*e S:i Soda granite oc<'urring south of Naranjito S4 Quartz ed traehytic structur(\ (a*oss(Ml ni<'ols... S7 Latite. showitig veins tilled with epidot(^ and iron oxides ss \n andesite pjorphyry with lai'ge jdienocrysts of plagioclase sun'oumh'd by a ixroundmass. showing the structure of a natural slag s'J Andesite porphyry impregnated with ehrysoi'(»lla. P»arrio Pasto, ....... . UO VOK TENTS OF VOLUME J x IMi»rite i)or[)liyi'y with pyroxene phenocrysts in a ici'ounduiass of iatli- sliaped feldspars < i>la.i?io{rlase) iM Olivine hasait •'- (;ross-i)e(l(leastal terraee lis (\-iyey in tlu^ liarraiupiitas-Cayey r.owland liM Tutr iHHls r.)\ JJfhoviifnix' s]». in slialt^s of tlie P>arran 'roi)o,i?raphy of the I»arran(piitas-Cayey Lowland i:'>r> Character of tlu* inieonformity hetween the P.arranuuitas-Cay(\v ami the Sierra dc* Cayey series 1.*J^ Con,u:louierate with an iiiiieous matrix 140 Ash shah's <'ontaininir Orbitolitcs 1 14 (Miert with d(»sieeation fraetures 14.", (^rystal tutf Un hithi<' tuir 1^1 Coamo SjjriuLrs iimi^stone ex[)osed in the I>esoalahra Lithitthdnmiou thalius in lon.u'itudinal section in ( •oam<» Si>rin^^s limestone I.Ki Coamo Sprin.us lian.!4:e loT lAthathinnniou in Coamo Sprin.irs limestone IoN AmphixivijiiHi in Coamo Sprin.i^s limc^stone Itio !*(}r()((if<(Us (■<))}<< iifriius in shale KJi* Shakes of the Rio Uescalahrados s(>ries Ki.*', N'alley of the (iuamani t(;s ('(M'ro (Javias. Coastal Terraee, Coamo liivei" !(»!> Felsj)athlc andesite 17- Auixitc^ and(*site 174 Auixite and(^site showimc feldspars comi>letely altered: au.L::ites unaltered., 17.1 Classy-au.Jxite andesite 17(> Olivine andesite 177 Olivine free hasalt... 17s Olivine hasalt 17t) La>a tlow containinii" pyroclasts of I'alcite which are surrounded hy irarnets 1S1 Flow hr Hornhiende andesite )*M\ HornhkMHle-auirite andesite P.M /'nrfnijscus concrHtricuy in tuffaceous shale Pjr> ^^llain of the Rio Grande de I.oiza near Carolina. .... 317 North-south protile through Porto Rico 318 I )iagram of the (4uanica district 318 The inner lowland at ( Juanica 321 The iinier lowland at Guanica 322 P>asal Tertiary south of Yauco, along the (Tuanica road 326 The gorge of the Manati. incised below the surface of the coastal plain. .. 330 Open haystack belt between Barceloneta and Arecibo 335 Apparent wave-cut bench at Quebradillas 3.36 Th<' inner lowland of the south coast, looking eastward from cuesta face ba{*k of Ponce 338 The Tertiary coastal plain lapping upon southern flank of Mariquita Hill. 339 The surface of the coastal plain between l*once-and Penuelas. 340 Reds of the coastal plain dipping slightly toward the oldland 341 Road cut at K9 H9 on the Ponce-l*enuelas road, showing relation of Ter- tiary to older series 342 Se River mouths at the north coast '^^- The coast east of Quebradlllas 3(i5 The uplifted beach on the south side of Desecheo Island 367 The uplifted beach on Muertos Island. 369 East coast of Mona Island 372 Sketch of Culebra and Vieques Island. 374 Muertos Island from the north 375 Maps Outline Map of Porto Rico showing distribution of district studies 26 New Base Map of Porto Rico, Complied from the latest Government Sources 36 Geologic Map of the San Juan District, Porto Rleo. Geologic Map of the Coamo-Guayama District, Porto Rleo. Geologic Map of the Ponce District, Porto Rico. Physiographic Map of Porto Rico. ERRATA I*age 58, line 33, and page 59, line 8, read Metis for Mctris NEW YORK ACADEMY OF SCIENCES SCIENTIFIC SURVEY OF Forto Mico and the Virgin Islaeds ¥OLUME I^Part 1 History of the Survey -i¥. £.. Britton Geological Introduction^ C F. Berkey Geology of the San Juan District-- 1), R. Semmes NP:W YORK: HISTORY OF THE SURVEY By JST. L. Britton 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 Eico was approved and referred to a committee consisting of Professors Boas, Britton, Crampton, Kemp and Poor, at the meeting of the Council in Kovember of that year, at which meeting the Council appropriated $500 annually for five years for the purposes of this investigation. Br. E. 0. Hovey and Dr. E. W. Tower, Eecording 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 oifered to assist the work, and has contributed $3,000. The Porto Eico Govern- ment was also interested in the investigation, and has since made two appropriations of $5,000 for prosecuting the work. The cooperation of The American Museum of Natural History, The Kew York Botanical Garden, scientific departments of Columbia IJniversity 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 Eico. The two agricultural ex- periment stations of Porto Eico, one at Mayaguez and one at Eio 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, >^oology and anthropology. Professor Crampton proceeded to Porto Eico at the end of 1913 and carried out a zoological 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 Eico.^ 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 SVIENTIFIC SURVEY OF PORTO RICO politicall}' a part of Porto Rico, and made the first represe^tati^ e 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 B. Lntz, made bo- tanical and entomological collections in the northern and western parts of Porto Rico and in the small 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 Botarucal Garden a paper on The Vegetation of Mona Island.^ In the summer and autumn of 1914, zoological collections were made over considerable portions of the island by Messrs. Roy W. Miner in marine invertebrates and myriopods, John T. N^ichols in fishes, and Frank E. Watson and H. G. Barber in insects and arachnoids. Many thousand specimens were obtained and important additious 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. Lntz in his List of Greater Antillean Spiders, with Kotes on Their Distribu- tion.** Richols has published some of the results of his work under the title Fishes I^ew to Porto Rico."^ The geological investigation was commenced by Dr. Charles P, Berkey and Dr. Clarence N. Fenner, wlio 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 ISTaguabo, 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 IST. 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 alg;p over considerable areas of the island. He obtained many thousand speci- mens of these organisms, which proved to be more abundant there than 2 Joiu'. N. Y. Bot. Gard., XIV, pp. 103-105. 8x\mi. Mo, Bot Gard., II, pp. 33-58, Pis. I, II. (Contributions from N. Y. Bot. Gard., No. 175.) *Ann. N. Y. Acad. Sci., XXVI, pp. 71-148. 5 Bun, Am. Mils. Nat. Hist, XXXIV, pp. 141-146. « Ann, N. Y. Acad. Sci., XXVI, pp. 1-70. (Contributions from Dept. of (.oolosy. (^)- lumbla Univ., Vol. XXV. No. 20.) " .Tour. N. Y. Bot Gard., XVI, pp. 33-35. BIUTTOX, 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 algae 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, w^ere spent by Dr. Britton, Mrs. Britton, Mr. John P. 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 soutli to Morrillos de Cabo Rojo and westward to Ponce find 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 ISTational 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 S. 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. ^« Bull. U. S. Dept. Agric. 1916, No. 354, p. 99. " 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 Eico. 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 Baiios de Coamo. Mr. D. E. 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 N"ew York Botanical Garden.^- Professor Stevens described and illustrated the species of the large genus Meliola as repre- sented in Porto Eico, under the title The Genus Meliola m Porto Eico, which includes descriptions of sixty-two new species and varieties. ^'^ Professor Crampton continued zoological field-work during January, 1915, especially in the northwestern portion of the island, at which time he supplemented previous collections by obtainino- 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 paiis of the island, adding some 15,000 specimens of insects and large num- bers of spiders to collections previously made. Mr. Eoy 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 Eaymond 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 archaeological investigations at several points during May and June, 1915, aided bv Dr. 52 Jour. N. Y. Bot. Gard., XVII, pp. 82-85. IS lUinois Biological Monographs II, No. 4, pp. 1-86, Fls. I-V. BRITTON, HISTORY OF THE SURVEY 5 II. K. Haebeiiiii, Dr. J. Alden Mason and Mr. Eobert 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 Eican children have been published by Mr. Leslie Spier.^* He obtained cordial cooperation in this investigation from the Department of Public Education of the island. He also concluded from his observations at this time that the Porto Riean 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 IJtuado, 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.^^ Dr. Haeberlin has published a paper entitled Some ArcliJBo- logical Work in Porto Rico.^^ 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 archaBological 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. ^^ " Am. Anthropologist, XX, pp. 37-48. '■' Jour. Am. Folk-Lore, XXIX, pp. 423-504. i<5 XIX Congress of Americanists, pp. 224-228. " Ann. N. Y. Acad. Sci.. XXVII, pp. 17-22, Pis. I-V. ^8 Am. Anthropologist, XIX, pp. 214-238. ^» XIX Congress of Americanists, pp. 220-223. G 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 alga^, principall}' along the southwestern coast from Ponce and Cayo Muertos to Cabo Eojo. 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 Eico 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 archaeological 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 petrogiyphs or rock- carvings. Mr. Bela Hubbard carried out a geological survey of the nortliAvestern 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, whicli 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 ISTew 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. xinthony 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 iS^ew Family of Insectivores.^^ ^ Jour. N. Y. Bot. Gard., XVI, pp. 210-225. ^Ann. N. Y. Acad. Sci.. XXVII, pp. 193-203. 22 BuH. Am. Mils. Nat. Hist., XXXV, pp. 725-728. BRITTON, HISTORY OF THE SURVEY 7 ±sew Fossil Kodents from Porto Eico, with Additional Kotes on Elas- modontomys ohliquus Anthony and Ileteropsomys 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 oiir knowledge of the flora ; he is now preparing a list of the fungi of Porto Rico. Dr. Basil Hicks Dutcher, TJ. S. 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.^* Another symjjosium was given at the meeting of December 14, 1914.^" At the meeting of the Section of Geology and Mineralogy on November 1, 1915, preliminary reports on field-work were given by Messrs. Semmes, Hodge and Reeds.^^ At the meeting of the Section of Biology Novem- ber 8, 1915, communications were presented by Messrs. Reeds, J. A. Allen and Matthew.^^ The Committee submitted a report of progress at the annual meeting of December 20, 1915.^^ At the meeting of the Academy held January 24, 1916, Dr. Boas, Mr. Aitken and Dr. Haeberlin^^ presented communications on ethnology and archaeology, and at the meeting of May 15, 1916, geological commimica- 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.^2 The final geological reports are being written, for the most part, by the ^ BiiH. Am. Mus. Nat. Hist., XXXVII, pp. 183-189. 2* Ann. N. Y. Acad. Sci., XXIV, pp. S69. -• Ann. N. Y. Acad. Sci., XXIV, pp. 398, 399. 2« Ann. N. Y. Acad. Sci., XXVI, pp. 433-436. -7 Ann. N. Y. Acad. Sci., XXVI, pp. 436-439. 2«Ann. N. Y. Acad. Sci., XXVI, pp. 456-462. "« Ann. N. Y. Acad. Sci., XXVII, pp. 250, 251. ^•^ BuU. Am. Inst. Mining: Engineers, No. 135. «i Ann. N. Y. Acad. Sci., XXVII, pp. 277-282. •"- Bull. Am. Inst. Mining Engineers, No. 135, pp. 661-676. 8 SCIENTIFIC 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. Yanghan, 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 Plants. — Dr. JST. 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. E. S. Williams. Ilepatics. — Professor A. W. Evans. Lichens, — Professor Lincoln W. Eiddle. Fungi. — Dr. W. A. Murrill, Dr. F. J. Seaver, Professor J. C. x\rthur, Professor P. L. Stevens, Professor H. H. Whetzel, Dr. E. W. Olive, Dr. John A. Stevenson. Algm (marine). — Dr. Marshall A. Howe. Algce (fresh-water and aerial). — Professor 'N. Wille. iSTo arrangement has yet been made for the study of Porto Eican diatoms. The zoological collections are being studied and final reports prepared as follows : Mammals. — Mr. H. E. Anthony.^" Birds. — Mr. 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. —-VTeliminsiT J work by Miss M. C. Dickerson. Fishes.- — Mr. J. T. ISTichols and Professor C. F. Silvester. Insects: Orthoptera. — Mr. J. A. G. Eehn 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. Eoy W. Miner. ss Mem. Am. Mus. Nat. Hist., N. S., II, Part 2. s^ Bun. IT. S. Dept Agric, 1916, No. 326, p. 140. BKITTOX, HISTORY OF THE SURVEY 9 MoUusliS. — Preliminary work by Dr. L. P. Gratacaj). Ascidians. — Dr. Wiliard Van Name. Crustaceans. — Mr. Eoy W. Miner and Dr. Wiliard Van Name. Annelides. — Professor A. E. Treadwell. Eckinoderms. — Preliminary work by Mr. D. M. Fisk. Bryozoaiis. — Dr. E. C. Osburn. Coelenierates. — Mr. Eoy W. Miner. Eepresentative collections of Porto Eican protozoans have not yet been made. The anthropological and archgeological documents are being written l)y 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 Eico, by Dr. Mason on the archaeological investigation of the very important site at Capa, by Dr. Aitken on the cave sites near Utuado, and hy Dr. Miison and Professor Espinosa on Porto Eican 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 wouhl be more complete if additional collections were made, but this is of course true all over the world. Considerable addi- tional zoological 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 archaeology 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 Eico to form the basis of a Nat- ural History Museum, and other portions will be forwarded to Porto Eico as the study proceeds. The remainder is to be divided among the cooper- 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 Eico, to the east and southeast. It is highly desirable, before our survey is brought to a close, that these should be studied geologically, zoologically and archseologically. 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 Eico 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 OP PORTO RICO By Chakles P. Berkey CONTENTS Page Introductory statement 11 Geological reconnaissance 14 Major geological features • 15 Rock formations 15 The Younger Series 16 Tlie Older Series IT PetrograpMc range 18 Structure 19 Relief features 22 Geologic history 23 Problems of the Survey 24 Expeditions 24 Classes of studies 25 General studies 25 District studies, with outline map 26 Special investigations • 27 Bibliography 29 New base map of Porto Rico. By Chester A. Reeds au INTRODUCTORY STATEMENT The Island of Porto Kico 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 Eico 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 SCIENTJFW SURVEY OF PORTO RICO top of El Yujiqiie 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 Eico 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 Eico may have to a former continental mass extending toward and possibly connecting North and South America, how^ever 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 Eico is very mountainous. Ji. central Cordillera extends nearly east and west, starting abruptly at the sea near Eincon 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 Eico. 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 Eico has been made the subject of a special study by Mr. Armin K. Lobeck and will soon be BERKEY, INTRODUGTION 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. Kumerous small islands lie along the coast. Two of comparatively large size, Vieques and Culebra^ which are respectively 20 and 7 miles in length, mark the continuation of the Porto Eican land mass toward the east. All are included as a part of the studies of Porto Eico. 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. Eainfall is very unevenly distributed. At the east end, near El Yunque, there is an annual ]-ainfall of 123 inches. On the other hand, at Cabo Eojo, 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 w^est 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, folh^wing subterranean channels in these limestones. There are no inland lakes and but few coastal lakes. 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 For discussion of this feature in much more detail, see the foHowinj? nrticlo by Douglas R. Semmes on The Geology of the San Juan District, Porto Rico. 1 ! ^^(JIE^TIFW SUR\I:Y OF PORTO RICO ()\er most r)j' tlie inland havc^ a direct infiLienee on the character of rock decay and disintegration and also on the (jiialitv of the soil. The a\'erage (hiily temperature is 80 degrees, and it rarely rises above iK) or drops kvlovv 'lO, while the maximum is said to be 99 degrees. In area Porto Eico covers ?u(u() square miles, and is therefore about tJiree-fourths the siz(^ of the State of Connecticut. It is roughly rectan- gular in outh'ne, with the longer axis east and west and in actual dimen- sions i.< a])])roxijnately 35 miles in average width and 105 miles long. Ir is tlie fourth in size of tlie AYest India Islajids. Porto Eico is very productive anerkey, 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 ])e made, form a part of the plan for this Survey.^ Seven such districts - A dPtaiUnl list of (hose topics and studies is given at the end of this article. BERKEY, INTRODUCTION TO THE GEOLOGY ]5 and areal studies and four general mvestigations were originally planned. Five of the district or areal studies have been made and one general investigation has been completed. MAJOR GEOLOGIC FEATIJEES ' 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 l)riet' outline of the more im])ortant geologic features characterizing the wliole island follows. Rock Foiimations Tliere is ao (jx(;(HMlingly large number of formational rock units in this field and a very great number also of rock types or varieties, and the con fusion as a c{)jise((uenoo is so great, at first sight, that it all appears a hopeless nunldle. This is <>sj)eeially true of the interior of the Island ratiuM- tban tlu^ coastal margins. In the higher interior regions igneous I'ocks and elastics derived mon^ or less directly from igneous action such as tulfs aiid aslies prevail, although formations of simpler sedimentary (\vat(n' laid) babit arc; 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 tlie north coast ^vest 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 w^ould expect them to be separated by a more or less profound break or imconformity. To this extent at least tlie first suggestion in an attempt to organize the complex structure of the island is correct. There are undoubtedly two very distinct 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, h; scji::xTiFJO suuvEy of pojrto rico there is a \erv (lis, marls and shales. This is a much more extensive and geologically important mem- ber than the San Juan. Subdivision is dou])tless 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 w^ide appli- cability. They have been, however, of distinct usefulness in all studies thus far made. The most commonly used are the following: 1. The Areciho llmesloiw upper limestone nu'mber on the north sid<^ of the island. 2. The ISan Srhaslian shales low(»r, shale member on the north side of the island, rl. ''Jlu^ J van a Diaz marls south side shales and marls near Juana Diaz. ■1. The Ponre Chalk beds V(M*v white chalks nrar Ponce on south side of the island. BMRKEY, INTRODUCTION TO TBE GEOhOtlY 17 The greater part of all these beds are satisfactorily (leteriniiied to be of Oligoeene age, but the latest studies indicate the presence of representa- tives of both Eocene and Miocene age as well. THE OLD Ell SERIES This iiichi(his a C()ni);)k\\' association of tuifs^ ashes, sliale, (conglomerate, limestones and a very great variety of intrusives and occasional hiva flows. Tli(\^e nre readily seen to b(^ (Miongh obk^r than the other series to have sii{fcr(Ml nuK'b additional modification of petrographic- charactcM^ and deformation, and it is comparatively sim])le also to determitie that the jncMubers of the series as far as they bear fossil evi(kMice seem to be con- tiiied to late Mesozoie ag(S ])erhaps wholly to the (Veta(!e(nis period. Th(^ {)\(\qv Sei'ies thus far has failed to show evcMi as (h'stinct lines of sub(h' vision as the Yonnger. IVrha])s there are breaks as great as that L>et\veen the Han Juan and tlie Arecibo formations of the Yonnger Sto- ries, but the structures are nuu^h more obscure, by n^ason of (hdormation annient in this case also to designate certain well marked units by h)cality names. Xo assum]>tion is made as to their extent or the possibility deserving recognition in attempts at correlation. The Kecon- naissance expedition made free use of such tei'ms to much advantage in \\w Held, and latcn" still others have been used l)y the investigators of special districts. As a matter of fact, the great difficulty found in the begiiniing in following any single tiehi unit very far or identifying it at oth(u- places made the use of many locality and arbitrary names particu- larly serviceable at that time. Subsequent studies have not successfully ehminated them, and it may well be that tlie accumulating proof of the great variability of all these formati(ms as well as other units will com])el the retention of such lo(»aI names. Among the terms that belong to the recomun'ssance stage aiid that bid fair to be retained are the following: IS xcn:\TiFia suu) i-jy of pouto rico 1. The Fajardo shales, a very widespread type of blocky shale. 2. The IMayaguez sliaU^s, similar to Fajardo shales in general stnic- tural habit, n. The ('oaino Tuff-Limestone, a hea\y limestone carrying abundant tuff fi'agments. 4. The Trujillo Alta Limestone, a very limited occurrence of dense limestone. 5. Tlh' ''Shred" Tiimestone, a name suggested ])y the appearance of the elder fossil form. (>. The Tia ]\luda Limestone, a formation that seems to mark a break of mor(^ than average consequeiu^e. i. The Mountain Tjimestone, of Hill — thin-l)e(lded, slialy limestones and limy shales of very extellsi^■e deveh^pment along some of the mountain ridges. S. Tlu' (^orozal Limestone, a peculiar local occurrence of limestone ])reccia at Coi'ozal. PETROGKAPHTC RA\(;K The pet rographic variety of this older series is very great, but th(^ ty]>es of large C()nse(pience are not numerous. They may nearly all be included within such group terms as limestone, marls, shales, sandstones, conglom- (n'at<'s, tufTs, ashy tulTs, 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 gi'aywackes and rarely some contact products as the chicd' badly modified typ(s. Although tlie range of different ty|)es when stated in this foim 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 ai'eal 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 nimiber of small units which alternate or change so many times in short distances that d(^tailed mapping of them, or even an attempt to represent this detail bv the most carefully constructed geologic cross-sections, seems hopeless. All ]7racticable representations of the geologic structure are necessarily i>eiH^ralizations, BERKEY, JXTEODUCTION TO THE GEOLOOY 19 ^taps of any kind eoyenng 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 seems 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 qiiality 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 th(^ soutli 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-])edded 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- positien, are also very common and there are a few large bosses several //:a I'l i'ic >■/ h'\ i:y <>i' f(urn) i:i< ' nHV ! iilr irlu.lmi: UTrii? nHloUIlt- of llliT I'f n< kiiHl i> II. .u 111. MiiM.r slrii.iiiriil (v.iiuv,: mi<4i a,^^ Xi^nolilhi.' iiirhiMnii^ in \\w ml ni-.n <•>-. nic .■xl,.|isi\..l\ ,!..u.l,.|.c,!. Snin.-liHi.- ;i sill ,.r .lik.- is lihTallv .m-..«.|.m! with tiiir rniu^i)ifii1> -^H rlusfly j.m-kcfi L.-viInt that t!i.^ wlml,' lia^ i.-|..n- ih.. ovnrnil uiihviir.l i!i.|N.:. nui.r of a liitV tliuii a hona ti«l.' nitriiH'vc. l,*.^^ [icaird iiisuc.-ii.Hi t.r tin- r-inirturf. Iihwcmt. Iia- rt'imncu fxcry .i<.iil.i a- i,. tlir ,->','iilial .•..nv.-liM-^ (.1 till- .■,h>Mnan<.n. A ratii.M' ivnia rkal.l. HiHHir -tni.-tiiiv III r!i.^ San Jir.ui iuniuiti.m. ultirh i> hrliru-,! i,, l,,- a r(,,iM,|Hlal.-.l .liiii.^ ^aiui. 1^ niiKtratr.! ni ih.- a.v..,,,i,an\ in- ll-air.-. It iti:i>'h f:) ^ I \ I i:i>ni r-fins to nn: fH'jti.oi.) 1' TT'^^^m^mmm^m. Ih.iJKi^ Vi Til,' |.)rs(;iir ri'li.-r Iratiiivs ..f l',,rt,. lii.-u an: all iIm.m; ,,r HHi|.|r .T.Ku.n i( tluf inferior la iiii'd ) ) Tbc development of an nnc^onrorniable overlyijig sei'ies of shales, nvf h'niestones and relatiMi deposits cliietly of organic origin, bi'ouglit to at! end by final ]'e~e mergence. (I } Tbe development of present surface features uiukn* stream erosion and marine marginal attack, witli modifications arising from oscillation of level. PROBLEMS OP TITK SIRYEY Hie prnblems that were snggestet to establish the subdivisions of the Youngci* S(M*ies and make paleontologic collections. New base map pre- pared (priblished with this ])a])er). .*>. IVIr. Douglas K, Hcmmes. Stmiy of the San Juan Disti'ict (Seiiniu^s. 1919). 4. ^Ir. Edwin T. Hodge. The Coamo-duayama Distri<-t.' (/•) Expeditions of 19irK 5. Mr. Bela Hubbard. Tlie Aguadilla-Lares District. 4 G. Di\ Cliarles II. Fettke. The Humaeao District.^ 7. IVIr. Annin K. Lobeck. A general stnistnct.+ •■• Reporr ready for ptibllcatioii. * Report interrupted l»y the war. BERKEY, INTRODUCTION TO THE GEOLOGY 25 Classes of Studies Tlie wliole list of studies of all kinds fall into three classes : (a) (leiieral studies^ covering certain features affecting the whole island. (h) Area! ov districf studies, with acxionipanying geological maps. {(•) SptH'ial investigations on prohlenis suggested by local conditions or tlic material collec^ted. GKN-ERAL STUDIES Among tlie genci'al (juestions which hav<^ been considered to })elong to the island as a whoh^ are the folh)wing: Xrtr llnse Map. — The making of an accurate detailed map, such as nn'glit )>c re])resented l)v topographic sheets of the kind pi"e])ared by the r. Si. (Jeoiogical Survey, is an undertaking much l)eyond the sc()])e and facilities of this Survey. Each investigator of a district has uniUnlaken th(^ correction of the maps available for his own area in enough detail for the ])ur])ose. These districts, however, aiv not complete to snch a point that a general relied' niap for the island could yet hv constructed from them. As a stej), therefor(\ preliminary to that result, the data of all ])reviously ]nd)lished maps, together with such, notes as wei'(» available from fitdd obser\ation, have Ikhmi compiled, under the direction of Dr. Chester A. Reods, in the form of a new relief map which is ])uhlished luMMnvith. I'hydoijraph.y of PovU) Biro. — After the reconnaissance and first dis- trict studies were made, it became itpparent that a general physiographic study covering the whole island would be y)articularly d(ssirahle. Tlie opf)ortunity to make a complete study of an isolated land mass, with a |)livsiographic history ])robal)Iy similar to most of th(» W(*st Indian islands, seemed to he particularly good. Mr. Armin 1\. T.ol)eck under- took this study and his work is completed. Trrfinry Hf rail f /rap] ly. — 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. I)r, Chester A. Eeeds entered upon the investigation by making a collecting expedition in the season of 101. ";. Tt was the intenti(ui to iiudude in this study a determination of the principal subdivisions and boundaries of the Tertiary strata for tlie whole island, and it was hoped that this could be done on simple enough lines and ])romptly enough to be of service to all of the men doing district 26 SVIEXTIFW SURVIJY OF PORTO RICO luappiiig aiifl making local studies. The problem has been found espe- eiallj' difficult aud final results are not yet readied. Iji the meantime the practical matter of mapping has been solved in each district as well as }nay be, and probably no full statement of the Tertiary stratigraphy ^v'ill now be attempted till all of these separate studies are available. Mineral Eesomxes. — Considerable money has been spent in Porto Eico 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 I'ew plac(\s now. Many ores of other metals are also formed as well as other economic pi'oducts. Almost none, however, have proven attractive as the basis of an industry, although much interest is attached to such possibilities. Mineral resources of sutTicient 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 g(^n(^ral study after all of ihe districts have been fidly investigated and reported. DiRTHK^T sM^in)n<:s, ^xrni outline map The basis of ail detailiMl iinestigations is the district or areal study, it has been found possible to divide tlie 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 cbosen, 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 l)asis the area of the wliole 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 ad|oining areas (see 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 ]K)int 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 Barraiiquitas into a northerly and a southerly district Scientific Survey of Pobto Rico and the Virgin Islands Volume 1, Part BERKEY, INTRODUCTION TO THE CEOLOOY o; The northerly one has for convenience been desigiuited 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 geologic map, forms a part of this bulletin. The south end of the belt, south of Barranquitas, was studied by Mr. E. T. Hodge. His 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 by 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. The 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. TIio geology of this disti-ict was studied by Dr. Fettke in 1916. It 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 corjier, occupying \he area north of the Humacao District, and may be caUed 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 {h) are chiefly concerned with pure science investigations connected with paleon- tology. Immense collections have been made and seem to be Avorthy of elaborate study. It is expected that they may ultimately form a volume on the paleontology of Porto Eico. A considerable list of special topics enumerated in the original Eecon- 2S i<('li:\TIFI(J i) Changes in eharaeter and composition of the igneous ])roduets al dinVrent stages in i^)rto Jiieo Aoleanie history. {/) I'hei-jnal s|)rings. ( // ) Stn would com])lete such work, and it Avould then be ])ossibl(» to make a final geological map of tlu^ island and to write file summai-y of its areal, stnu^tural and economic geology and its geo- logical history. A completion of it to that consummafion may be regarded as the immetliate ohjecd of these geological f\v](\ studi(^s. The |)aleontologic studies, in so fai" as they are ]iec(\ssary to the liistorical treatment and stratigraphy, are to he included in the ge(dogic iuvestigations. Siihse- quent studies of all kinds and to any extent may he based on the collec- tions, and additional investigations along |)aleontologic lines will then Ix^ includccl in a separate ^otume under paleontology. lil]HKE\\ INTRODUCTION TO TJIIJ (HJOLOGY 99 BIHLIOCniAPllY I>ERKEY, Ci1AHIJ:S P. 1915. Geological reeoniiMissaiu'e of I'orto Rico. Aim. N. Y. Acnull. No. LM, lHv. Fstiy. IT. S. Dept. Agric. 1899?>. The value of l»orto Kico. Forum. XXVII. pi). 414-4P.). 1899c. The geology and i)hysical geography of Jamaica. P.ull. Mus. Com)). ZooL, XXX lY. Skmmes, Douglas K. 1919. The geology of the San .luan district, Porto Kico. Scient. Survey I'orto Kico and Mrgin Islands. N. Y. A. S., 1, pt. 1. ]»p. MrMK). Wilson, H. M. 1899. Water resoui'ces of Porto Kico. Water Supi>ly Papei- \o. .'^►2. W S. Geol. Survey. 1899a. The engineering develoi>ment of I^orto Kico. Engin. ]\Iag.. XA'fl, pp. 602-621. 1900. Porto Kico; its topography and aspects. .T(mr. Anu Geog. S<»c.. XXXIT. pp. 220-2.^S. >'. lOlT), for the I^ew York iVcadomy of Sciences and the Porto Kican (lovcrnnioiit, flic American Museum of Natural Ilistor}^ cooperating, it s(M^m(Ml desirable for plotting results that a small outline map of Porto Pic<^ should he prepared. During October, 1915, such a map was drawn at The Amcriciin Mus(uun of Natural History by Mr. A. Briesemeister under my direction. Most of the data for the base sheet was obtained from i\ large map which had been prepared by the engineers of the Interior Department of the Porto Rican Government. The four-sheet editio?) of th(^ TL S. Coast and Geodetic Survey and the XL S. Post Poute ma]) of Porto Pico were also used. P)efore the end of October a solio pi'int edition of one hundred copies of this new base map of Porto Pico was publislied l)y Tbe American Museum of Natural History. Com- ])]imentary copies of the preliminary edition were distributed to the membei's of tlie Porto Rican Committee of the New York Academy of Scienc(\s, to certain officials of the Porto Rican Governraeut, to the various held 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, 8000, 3500, (000 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 vai-ious sources, chii^fly the TJ. 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 pri^pared by the Irrigation Service, the IJ. S. Geological Survey's topo- graphic sheet of the Luquillo Forest Reservation, together with H. M. Wilsoiv's topographic map of Porto Rico, prepared for the IT. S. Water Supply and Irrigation Paper No. 32, 1899. Numerous photographs by Professors C. P. P>erkey and H. E. Crampton of the Porto Rican Com- mittee of the New Y^ork Academy of Sciences as well as a large number bv mvself were of considerable assistance in the preparation of tlie topo- urapbic sbeet. Fifty solio print copies of tliis contour map were issued V OUT ME I, Part _ 65^30' 20' 10' ^}i » ;__ I ^ I I » NEW BASE MAP PORTGRIGQ' -Xompiied frorn the latest Government Sources ^"^Ey-ckESTER A.REEDS aTidA.BRIESEMEISTER October 1915 18° 30' i);iind8 ^&. i^\ \ no. kf' CrossCay I E Y^ Q o- js ' Roads under Construction .,,/u-v---*x...-j..«ai. Roads to be constructed ._-._ — — Native Roads 20' J,./, 1^ ^ .^. ■v^:. a REEDS, NEW BASE MAP OF FORTO 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 Kican charts of the U. S. 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. THE GEOLOGY OF THE SAN JUAN DISTRICT, PORTO RICO By Douglas R. Semmes (U)NTENTS Synopsis ;•».■") I iiti"c)(lii('tioii '{(> (i!eo,sj:rai)liic Location :{7 Nntnral History Survey of Porto Kico .'{7 San Juan District :;T ri)ysio.i;rai)liy of tlie Island :5S ( 'oniplex Mountainous ( )](llan(l , :;s INnicplanation 40 The Coastal Plain 40 Mature 1 )issection 41 Kecent Submergence and U])lift 41 PliysiojL^rapliy of tlie San Juan District 41 'I'he I )une Aiea 41* Tlie Playas 4:i Tlu^ '^rcM'tiai-y Limestone P>elt 44 Ten-aces 4() Tlie Ijnier ] ^owland 47 Tli(^ hiterior Mountainous Keju'icui 4S Incised Meanders 40 Stream Capture 50 l*en(^plane ."iO Hock Formations .">1 YounjL^er Series ry'2 liecent Deposits .■)2 Unconsolidated Lime Sand 52 I'laya I*lains 52 I*leistocene ( ?) Deposits 5;j San Juan Formation 5:5 Age 55 Tertiary Limestone Series 55 Arecibo Formation 55 A^^' '. 57 Older Series (;() Kesidual Soil and Depth of 1 )ecay CJl Corozjil Limestone 02 Ia\ Muda Limestone 64 A j^uas Huenas Limestones 04 Limcv^t one at K 29 (j.-^ (•>3) 31 XCIFjSTIFIC *S7 7iM7;y" OF PORTO h'KJO I'age Juan Ascencio Chert Beds (>5 Corozal Jasper Bed C>^» Shales (>T Sandstones ^>-^ Conglomeratej^ ^^^ Tuffs Tl Age T2 Summary 75 Igneous Rocks TO Modes of Occurrence T(» Lavas 7(> Sills 70 I )ikes 77 Stocks and Bosses 70 Texture 7i) Composition 80 Vitrophyrs 81 Rhyolites 82 (Iranites 82 Quartz Latites and Khyo {nnlesites 8.*] Quartz Monzonites 84 (Jranodioritea 85 Dacites 85 Quartz Diorites , 85 Trachytes 8(5 Syenites 80 Latites (Trachy-andesites ) 87 Monzonites SS Andesites , 81) Diorites 1)1 Basalts 1)2 Olivine Basalts iV.] Summary 9:* Structural Features 1)5 Unconformities 95 Faulting DG Folding 1)S Metamori)hism 1)S Minor Structures • 98 Cross-bedding 9,S Solifluction 9S Stratigraphical Summary 99 Mineral Occurrences 102 (lOld 102 I *lacei*s 102 Auriferous Quartz Mines lOr, Platinum j04 <>>PIH'i' 104 >^/';j/ ]//;>s, a/joLOGY of the ^an juan district 35 Page Lead 105 Manganese 105 Road Metal 105 Building Stone 106 Guano 106 I llustrations 106 Cross-sections 106 Maps 106 Acknowledgments 107 bibliography 108 SYNOPSIS The area (leseri[)ed in this report, which lias 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 east 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 ])hysiographic history of which may be regarded as essentially the same ns 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 vslightly sul)merged and partially uplifted, erosion continuing in the interior from tlie time of first uplift. The formations of the district may be primarily divided into the yomiger 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 r the general aspects of the country appeared in currc^it periodicals and in 1 Dorsey (1002), HiU (ISOOff). n899r), Wilson (1809), (1900). procrtMlings of lejinied societies. Interest in Porto liico, however, soon waned, and from 1902 to 11)15 nothing regarding its geology was pub- Ijslied. In 1015 a paper by C. P. P>erkey appeared in tlie Annals of this Academy, whi(i]i gives the first detailed and ])urely geological description of the island that lias yet ])een written. (}i;()(;ijAPii K* Location Porto Pico, the smallest and easternmost of the Greater Antilles, aver- ages .')5 miles in width and 100 miles in lengtli, presenting a regular rectangular outline three times as long as broad and alined nearly ex- actlv east-west. Its shoreline is nearly straight and quite regular. The coast is usually low, Avith a few low ])romontories. The fringing keys and deep indentations characteristic of a more youthful stage in coastal de\'elopm(^nt, aiul so abundantly developed on the Cu1)an coast, are en- tirely wajiting. Its area is ruriO square miles, just 500 square miles less than the area of Jamaica, or about three times that of Rhode Island. Its |M»|)ulation, considered as a whole, is the densest of any country on the globe. Natuilvl ITisrouY S(jkvi':y of Poirro Pico In 11)11 an a])pr()[)riation was ]nade bv tlu^ Insulai* Government of INtrto Pi(M) for the establishment of a Natural History Survey which was to be carried on in conjunction with the New York Academy of Sciences. The geological ])hase of the survey Avas begun in P) 1 1 when Dr. Berkey an(! Dr. Feinu^r s])ent a moidh on the island, making a geological recon- naissance, preparatory to a snbsequent and more detailed survey. The following year the writer was assigned to Wm^ San duan district to begin 1ln's more detailed work. Sax Juan DisTincr The region selected may best be called the San Juan district, as San dtian. the ca])ital, is situated in the northeastern corncM*. The district is that area comprised between longitude ()()° 05' and ()r)° 27' west, and an •■ast-west liiu^ through the town of Pjarraiupiitas about 21 miles south of die northern coast. The areal extent of the district is roughly 500 square nnles. A correspcmding area of similar width to the south was studied It the sanu> time by Mr. E. T. Hodge. In this way a belt 25 miles wide was sur\eyed entirely across a ty]u'cal ])ortion of the island. Three "»'»nihs were spent in the liidd, in which time a topographic map was "it>tructed, the mineral resoui'ces stndicMl, and the geology plotted in as .*)S srjtJXTJFic SI R\ i:y OF roRTo lavo iinich detail as possible. consideriD^- the sliorlness of tlie lime and tlu size of tlie area involved. 'vwv: iMivsi()(MiAniY OF Twi: island ^V\\v i^cMieral eondiiuration and io])oii,ra})liy of the island liaxc been well deserilx'd by sexeral writers. Doi'sey (UK)'^) bas written an ad]nii'al)Ie description of the several types of topoiira|)by one meets on erossin:^- tJie island, witli an es])eeially detailed deseri])tion ol' the limestone top(\u;raphy ot tlie coastal ])lain. Wilson (IS!)!)) also has a'iven a. i^ood <;-eneral de- seription ot the physical asjjects. and Hill (1. 40). In the western ])orti()n of th(^ island the divide is double, where it is ])arted l)y westerly tlowing sti'eams. Near Adjunta- the two divides join at the tiead waters of the Anasco Jliver to form a single ridge, whicli continues to (^ayey, where it iirst swings southward. and then sharply to the uortheastern corner of the island. The Lnquillo range forms another westward ext(vnding brancli of the divide nearer th'' nortliern coast. The texture of the mountainous topogra])hy is uuMlium to fine, exc(^]» for certain lowland areas of coarser texture. Idie intei'ior topogra])hv r •v'/-;!/. !//•>'. <:FJ>iJH;y of the s\\ ./i\\.\ i>i>;Th'if"i' ;->,;i prciktininiiiitly tlic ridge or vurlilUn \\\m^. The slupes rtre cxtrrturdii'iarily sUTp. slojM'H of .KM4I demves liuin,ff oftc.ii seen. ln,>lwfeii thivc ridu-en thi; >tmnns run in V~ of the valley wall^ are very r^teep, lo h.' luiiiul. T.lic i^irvmm iiurth uf tin- divide nrv very miiiu-n.u.^ and of lai'.i!!' '.^olimif. diu' to tJie ahundiint |ii'('fipitrtti(Hi of Hit- large per rciu id' ruii^uir. IjoisiL til*' hirgcst river, rises milv eiyid luileH north of Arrovo ,el'i,r Ihf innrvr >lai,i irt K . "■n llie *w!ng in hirge meanders over the Hat playu plains br-rikn-ing tlie enast. Ttiiis a ty])ieal stream su«-li as the IMata nn tlie northin-n enast imu- show ■ vf-rv stage in development from y;l|-( ..f till' (lislrirf. hut ,1 fiirlluT \\v>t tli.iii till- S;iii .hiiUi 'li-iri .]>,. lln> nri-iii ami wniixr of {In.' Pl.-isUM-eiic n> well iH thr m-Mlt. <;uitri<'l. S,. pa rale. I 11, ihi: sea l.y th.' e (.1: the plava -fthiins is i.rcasitmally Inniken by low, rtnnnle.d liihls ■r'lln. TeriJaTY liinesluni-s rising al.nve the alluvial (Rig. :}). These inie.stcme Inlls'aiv isolate.! rnniiiants of the coastal plain here buried bt- iealh the recent dt^p'«>J>- khving tn the slight eh-vali-.n llnit t1iey atrord, ii-.v^. ilie blister iiig bear of the snrr(mndiiig [.dains. ibey are seleeted as •wn and dwelling sites, llotli D.trado ami T<«t Baja. llie only twe. t..\vns 4 1 ^cih'XTiFK' ,sfini-:y of porto h'fvo situut.'d in thi; center of tlie i}hipv<, iiro lniilt open tlicwc liinestoiu' rcii^ luiiitr-. Otlicrs jirc vh.omi as nitcs for the imljvi.lual ol' the njitivcH. The plava pUiiii^ follow the tliiTH' ]>n"!ir'ii)a] viillcp of the Ciljueo, I'lHtii, ami BavrtmoH Ihxevi^ for some -lishuicc inlHiul. and in tho case o( \hv IiitJrr two cxtond well bovonil the liiiieHtouc belt. The --eolooieal history of the formajion of th.e ].kTa plains has, no (lutibt. been e direetlv into the irne alhivinl phiins of the river valley. .Fust flow important a rblu tlif sen hiis played in ilieir formal ion is \i (lelinitely kjiowii. It is the writer's opinion, Iiowever, that both faeto have been intluential. This point wilH.e further disenssed helow. Tiu-; Ti-.ui"iAi!Y Lj,MJ-:s:ro>.i' Hiihr As the northern eoasi of Porto Wwo is approaehed, one readily distin- _mn'sbes two kinds of topti_<:-ra)ihy ; tlie riig'"t'i| oulliiH'. iiinl .«n tlcu^^oly cov- Tc'l with trnpifiil Yi!«ii'tjitinii t'hrtt they Jorin thi; most iiuu'cessihlo aiitl !ii|niH^rthlc' re<>-ioiiH oi' the district. Slopes f»f }0" aro quite comiiiuii iiinl H-,'!i^ioiinlly \i^rtiortl faces of linu'stoiic risiii^u- !0 or 21) iV-ct jito to he seen, rhuiigh froni a, (listaiu-c th,e hiJls appear well romuli'il, yet at eloso range hey arc exceed i ugly roiigii aiul Jagj^'eih tuHl arc. as one of the .Vmericaiis iviiig ill the vi<'inity expressed it, "very hard to seTHiubk! up."' The 111 usual appearance t»f these limestone hill< was early iiotieeel hv the iia- ih».(l l.y li. 'cs. w'lu) call them pr jiiiui.-^ or ciiciiniher^fihapcd hills. I>crkey has nsct • • term "haystack hiJIs.*" a term pe.'uliarly fitted to piclure their a'ppcar «v, rising ahniptly a> tbe.\ do from comparatix'cly level plains (Fi.u;. I 1 r»oth Dorscy (l. — }iif(i(c of (■i(est- 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 moimtainous area one is im- pressed witli 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 hkewise closely and deeply corrugated l)y ravines and gullies, the wliole region assuming very mucli the appearance of a wrinkled handkerchief, a simile said to have Nf;j/ !//>•, fiHoijjav OF Tin-: klv .hwj niminvT 4!i Ivrii x\ \a:.v\ fiire. A, few ea>os weiv noted where Home adJiiHtmynt: had taken pliicc, hot nowhere \va> it eoiiieii(vus. Altlmngli the iTunintaiiuju.- region H nnderlain hy n complex of formations of miieli variety, jet tliere is little if'iH'ed fur a short dislanee as a. poorly tliseeTnihle rid.a'e. and it was ne^ / UH'I tllV illf„re .,f ■leed iluit The higliest points were iisnally underlain hy hJ^'hly indiinited -dieeoos tiillV, aSj for example, Torreeilh', .northwest of Ihirrampiitas. and •i''leelial, some distaiiee soiitli of* 15avamon. oine of the streams have ilevelo|X'd dee-plv intrenched meanders as .' puss out from tlie mumitainoius oldland. 1'he Itest example is tliat 50 SCIENTIFIC SURVEY OF FORTO RICO of the Orocovis Eiver 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. Kear Comerio, however, there is a wind gap that was evidently at one time occupied by a tributary of the Plata Eiver. This tributary, now represented by Mora Creek, formerly flowed from the southeast through the wind gap and occupied the upper valley of the Arroyato Eiver (see topographic map). Subsequently another tributary of the Plata, work- ing down from the north, intercepted the larger stream, forming the present Arroyato Eiver, w^hich joins the Plata at K 23 on the Comerio Eoad. 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 ISTaranjito. The peneplane level, occasicfnally 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 w^ould appear that the peneplane surface was slightly upwarped along the southern edge of SEMMES, 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 regar"ded 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 v^riter 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 situ and the formation of a thick soil mantle, which would tend to destroy the minor irregularities in the skyline. EOCK FOEMATIONS The format ional units of Porto Eico 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 f their respective ages, as follows : 1. The modern sand dunes of the coast and the adjoining playa plains. 2. The Pleistocene (?) San Juan lime sand. 3. The Oligocene limestones and shaly limestones (Arecibo formation). 4. 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 somev\rhat complex, and showing considerable variation laterally. The lower shale member is evidently a separate for- ^national unit, merely representing a local .development, which is not Sound in the San Juan district. A subdivision of the underlying older series, however, is .quite another matter. The complexity of tlic forma- 52 SCIENTIFIC SURVEY OF PORTO RICO tioiis 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 occur 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. ilt 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. si-:m'mi-:s. nFjiuxiv (u-' tiik k-i:v ,/c:,i:v ihstuict l'LK|i huili. It Iiere forms a >rrikiii_y- pnHiioiitMry lluit I'XtiMnls as n spit sevei-al mih^'S out J"riu' walls uf tlu- i-asth- hfiii^ hiiilt upmi the very ^hp- ..r tla (Fie. s). The San Jiiaii formation '<\-> seen at this point is a very porons. medinni I'l coarse graJned faiuistone eomposed of miTnite fragiiien,ts of shells and '.vell-rcroiided. quartz grains, hennd tcjgetdier with eahrareous cement (Fig. •^). The eal-her. hut in nn casc> did Hi-ll-:STI FH' t^lini'.X OF I'ftUTi) RICt ii; n,.n>tit.ij{(; as iiu!c-li as liftj per cent of the rock, in the virtiiiiry nf ^Sijii .liiaii two distiiK;!,. types ot: the roiinatinii were IV.uihL Vim. that which oeetirH well above sea Jevel near ^h.rro (•a>tic. At this pniiit tlip lime sand is exeecdingly jioreus. The itciucnrin.u^ material re spac-es is a.l>mit W-:W [u-r eeiit of the entire rocrk. The >ci'on-(l variety uf lime sand was taken frum a qiia.rrY neiir Borin a Imililm.e- sr,o!ie. It is evident, fherehuv. that the of ecmeiitation is (iependent upon rhe hmgth c,r tune Uie h.rmati 'been exposed to the free eiri-iihii ion of calearcMnis selntions. Ttie pceiiuii of the fornialiuii, hein-- rc-eh'\ated jiftcr oe1\ a, short pe ;-nhmer2enee, innv shows only tlie initial >la,ii-es ot .••onx.lidat loje Ihi- lower portime still siihran.d, ha- lamse.jnlafed iirto a dense m dural.le rock. The t|nestjoi! then arises whether lie- p.rro.:it\ ..f lie, i.i.rtion (W tlie forinHlieaj !.> ne»! due to suhscipienr leaehiiej; j-a.!eer 1 SEMMES, GEOLOGY OF THE SAN JUAN DISTRICT 55 initial poor cementation. A microscopic examination of the lime sand, however, shows no evidence of any appreciable amount of subsequent leaching, for a subsequent dissolution would have affected the readily- dissolved calcareous fragments as well as the calcareous binding material. West of the extremity of the San Juan spit, the continuation of the San Juan formation can be traced by a series of islands, the largest of which, Cabras, rises just in the center of the harbor entrance. Small fringing islands of this type, wholly composed of the consolidated lime sand, can be traced along the coast far beyond the w^estern boundary of the district. All the headlands and points that rise above the general level of the coast are likewise composed of this material. Throughout this entire area one finds that the lime sand is characterized by very pro- nounced cross-bedding of an eolian type. This cross-bedding character is well shown in the face of the promontory below Morro Castle, as well as in numerous other localities to the west. The eolian type of cross- bedding, together with the fact that the San Juan lime sand is almost everywhere associated with modern dune sands, indicates that it was for- merly of similar character to the modern dune sands, merely having been subsequently consolidated. Age. — The exact age of the San Juan formation is uncertain. None of the modern sand dunes shows even the initial stages of consolidation. Indeed, much of the material composing them appears to have been de- rived from the destruction of the San Juan formation. Moreover, evi- dence of the final oscillations of the coast is clearly seen in the cliffs of this formation. Large portions of the consolidated sand still remain be- neath the sea, so it is evident that the formation was formed before these coastal movements occurred. The formation contains no conclusive faunal evidence of its age. The shell fragments are so minute that none could be determined. Occasional foraminifera occur, but these proved valueless as an index of the age. The formation has been regarded by Berkey as being of Pleistocene age. This conclusion is derived from its general appearance, situation, and close association with modern dune sands of similar composition. Indeed, the upper portion of the formation might possibly be post-Pleistocene in age, though as yet no direct evidence has been found to support this view. TERTIARY LIMESTONE SERIES Arecibo Formation. — Underlying the San Juan formation, but sepa- rated from it by an extensive erosion interval, is the Arecibo formation, so called by Berkey from its type locality, the town of Arecibo. The 56 SCIENTIFIC SURVEY OF PORTO RICO formation consists of a series of reef and shell limestones alternating with layers of calcareous shale. Towards the base of the series the shales become predominant. In the vicinity of San Sebastian, in the north- western part of the island, there is locally developed beneath the Arecibo formation a series of dark, lignitic shales, quite different from the yellow- ish, calcareous shales that occur in the base of the Arecibo in the San Juan district. No equivalent of these shales could be found in the San Juan district. It is the writer^s opinion that the San Sebastian shale is merely a local development, which is not equivalent to the Arecibo, prob- ably being much younger in age (see discussion of age of younger series). At Juana, Diaz, on the southern coast, a similar shale member is to be seen. At this point, however, the beds dip as steeply as 36"", according to Berkey (1915, p. 13), which would seem to indicate either that they underlie the Arecibo unconformably or that they have been tilted by later movements. In the San Juan district the Arecibo formation dips 6° to the north. Its maximum thickness is not developed, but towards the west- ern boundary it is at least 500 feet thick. It extends entirely across the district, forming a belt several miles broad on the west, but wedging to a mere line of isolated hills to the east. Much of its former extent has, no doubt, been destroyed by erosion, but it still covers an area many times larger than that occupied by any other single formation. Along the valley of the Plata, where a good section of the formation can be seen, it consists, in the upper part, of a series of white reef and shell limestones of medium density, with occasional layers of yellow, im- pure, shaly limestone. The shaly layers increase in number and become essentially light-colored calcareous shales towards the base. The basal shales are of this character in this locality, and are entirely unlike the dark lignitic shales of the San Sebastian region. East of the Plata Val- ley the base of the formation is not exposed, but there is no evidence that its basal shales differ in composition from those seen in the Plata Yalley. The Arecibo formation as a whole appears to be a structural unit. Al- though it is not uniform in character and composition throughout its vertical extent, yet there are no unconformities or erosional breaks, nor are the variations in general appearance distinct enough to warrant a closer subdivision. Since the formation varies laterally as well as verti- cally, no specified section would hold true for the entire district, yet as one passes over the formation certain general changes are observable, which are continuous throughout the district. The upper part of the series, as has been noted, is characterized by the predominance of a white or pinkish, chalky, poorly bedded limestone, partly composed of shells. Locally this limestone assumes a hard, dense, and massive character, being SEMME^, GEOLOGY OF THE (^AN JUAN DISTRICT 57 quite brittle and ringing when struck by a hammer. It is in this phase of the limestone that the caves, which are so numerous through the lime- stone belt, are developed. The absence of shaly material makes it readily soluble by underground waters. Locally the upper purer limestones show the characteristics and content of a coral reef. Near Morovis the lime- stone has such an appearance. Close examination shows that it is com- posed almost entirely of corals and is even more irregular and massive in structure than the white, chalky limestone. On passing downward through the series, one notes that the bedding becomes better defined and occasional layers of shaly limestone are to be seen. Thin, shaly layers occur even in the highest beds, but they do not become noticeable until better developed towards the base. In the lower portion of tlie formation the shaly layers become predominant and the massive, purer limestone is entirely lacking. The base of the series is entirely composed of calcareous shales, which are porous, coarse-grained, and well bedded. Such a suc- cession would naturally be expected under the conditions which seem to have prevailed. After submergence the coarser, shaly material would be laid down first near shore, followed by finer shales and shaly limestones, with occasional beds of purer limestone marking temporary periods of clearer waters. Finally, the upper limestone beds and coral reefs would be deposited when clear-water conditions had been established. Age. — The fauna of the Arecibo formation has never been carefully studied. The fossils are as a rule poorly preserved, nothing remaining but the internal molds which are rarely determinable. The older series was formerly thought to be Paleozoic, but the limestones of the coastal plain were early recognized to be of Tertiary age. In 1868 Cleve (1883, p. 189) first approximately determined the true age of the older and younger series. He stated "that the island of Porto Rico consists largely of very thick, almost undisturbed limestone beds of Miocene age; but in the interior of the country, around Utuado, rocks similar to the Cretaceous of the Virgin Islands are met with." In 1898, after a reconnoissance of the island, Hill concluded that the ages of the Tertiary formation were as follows (Hill, 1899a, p. 109) : The upper part of the Pepino hills is made up at their surface of a rather hard lime marl full of coralheads, with occasional indurated strata of firm white porous limestones. These rocks (the Pepino formation) are of Miocene age, as determined by Mr. T. Wayland Vaughan from the corals collected by me, similar to certain rocks of Antigua hitherto not known in the geologic sequence of the Greater Antilles. Their tilted position, standing at 1200 feet where they meet the older volcanic mass, testifies to the great geologic move- ments which have taken place in the West Indies in late geologic time. Below this limestone, which is at least 100 feet thick, are fossiliferous 58 SCIENTIFIC SURVEY OF PORTO RICO greensand marls of undetermined age (Eocene or Oligoeene), which in turn rest upon a great thickness of thinly stratified reddish lignitic clays and sands of Eocene age (the Richmond formation) which outcrop near San Sebastian, Guatemala and Mocha on the western end of the island, and near Carolina on the northeast coast. The pepino formation is in part equivalent to the Arecibo. No green- sand marls were found in the San Juan district^ but these probably cor- respond to the lower shaly Arecibo. The lignitic clays and sands are what has since been termed the San Sebastian shales. In the older lime- stone beds of the interior, Hill mentions the occurrence of a Cretaceous fossil (Rudistes)^ thus confirming Clove's earlier supposition that the older series was of Cretaceous age. Through the aid of Dr. William H. Dall^ the material v^hich the writer collected in the San Juan district, as well as some of that collected by Dr. Berkey the summer previous, was roughly determined. The material consisted almost entirely of internal molds, some of them being so poorly preserved that even the genus could not be determined. In only one case was a species positively identified, but the accumulation of evidence from quite a number of genera, as well as the general appearance of the forms, made the determination of the ages of the respective members of this series fairly reliable. The forms studied should be divided, according to the locality from which they were collected, into three groups : 1. Collected by the writer from the base of the Arecibo, near Toa Alta and from the upper part of the same formation near Yega Baja. The forms from these two localities are so much alike that no attempt was made to distinguish between them. 2. Collected by Berkey from the Ponce formation just northwest of Ponce, on the southern coast. 3. Collected by Berkey from the San Sebastian shales (upper portion) near Lares. The fauna from the Arecibo formation consisted of pelecypods, gastro- pods, and corals, of which the following genera were identified : MeAris trinitaria (Dall), an index of the Bowden formation, upper Oligoeene of Jamaica, found throughout the Arecibo formation in the San Juan district (PI. II, la, Ih), Pectens^. (PL II, 5). MiWiasp. (PL II, 2a, 2h). Haminea sp. Yery abundant (PL II, 3a^ Zh). Oyprcea sp. x4bundant (PL II, 4). Atnaiiropsis sp. Comis^, (PL II, 6). .1 m pulina sp. N.-^ i}i' I'm-: AIM SEMMES, GEOLOGY OF THE SAN JUAN DISTRICT 59 Strombuss^p. (VIII, 7). Orbicella aff, cavernosa (Linn.). Fungid corah not determinable, but similar to those found in the Oligocene of Antigua, Anguilla and Oaba (PL II, 8). Venus s^, (PL II, 9). Although only the first of these forms may be regarded as even an ap- proximate index, yet the fauna as a whole from its general appearance is regarded by Dall as Upper Oligocene. The occurrence of Metris trini- taria at the base as well as in the upper portion of the formation would indicate that the entire Arecibo formation as developed in the San Juan district is Upper Oligocene. The second group of fossils was collected from the Ponce formation on the southern coast. This material was also so poorly preserved that the genus could not always be determined. This group includes : Lucina sp. Lucina sp. small specimens much like forms from the Chatta- hoochee (Middle Oligocene of the Gulf Coast). (PL II, 11.) Pecten sp. like P. thetidis (Sowerby). (PL II, 10.) Fasciolaria (PL II, 12). Amauropsis ocalana (?) similar forms in Ocala limestone, Vicks- burg formation, lower Oligocene of the Gulf Coast (PL II, 13). As the relative position of the specimens in the Ponce formation was unknown, the geologic range could not be determined. It is probable that the specimens were collected from the lower portions of the forma- tion. These forms at least indicate that the formation is lower to middle Oligocene and that it is in part practically equivalent to the Arecibo formation of the northern coast. The third group was collected near Lares from the first shell bed of the San Sebastian shales. This shell bed is located in the upper portion of the shales. It contained : Venericardm sp. Ostrea sp. Conus sp. None of the forms of this group could be used as an index of its age, but from their general appearance Dall concluded that they were lower Oligocene or possibly upper Eocene. Therefore, since these forms were collected from the upper part of the San Sebastian shales, it is probable that these shales are, in greater part, of lower Oligocene age. (JO HCIf'JXTlFIC ^UR] f]Y OF PORTO RICO Older Series IFnderl}dng the Arecibo formation is a complex series of sediments of both aqueous and volcanic origin^ intimately associated with numerous igneous rocks. It is this complex that Berkey has termed the older series^ since it is unconformably separated from all the formations that have been described and is in appearance much older than these strata. The older series outcrops in all parts of the San Juan district south of the inner lowland, an areal extent of roughly two-thirds that of the whole district. The contrast in appearance of the two series is strikingly evi- dent as one passes abruptly from the nearly horizontal beds of the Arecibo formation, showing comparatively simple structure and only minor varia- tions in lateral and vertical extent, to the steeply tilted beds of the older series, where sediments and volcanics of all varieties are dissected by an infinite number of igneous rocks, both intrusive and extrusive, ranging in size from small stringers to major intrusives of many square miles in extent. The subdivision of this intricate series is an exceedingly diffi- cult task. Many of the formations are of such insignificant thickness that they would necessarily have to be grouped to appear on a geologic map of moderate scale. Such grouping would be on an arbitrary basis, for the formations involved do not naturally fall into larger groups. Con- sequently, only generalized subdivisions have been made on the geologic map, the detail in structure and composition being shown on the accom- panying cross-sections (PI. IV). The rocks of the older series include: Sediments essentially marine. Sediments essentially volcanic. Igneous rocks. ^larine sediments which have been wholly derived from the land through the ordinary processes of erosion and stream transportation are almost unknown in the older series of the district. Practically all of the marine sediments contain volcanic material. Some are composed wholly of volcanic material cemented by carbonates. These sediments have been well assorted and bedded, and often contain marine organisms. The marine sediments — that is, those that show more strongly the character- istics of marine rather than those of volcanic sediments — include lime- stones, shales, sandstones, and conglomerates. These form only a small percentage of the total thickness of the older series. Occasionally shale and conglomerate beds of 100 yards or more in thickness are to be seen, but the limestone beds are usually less than 100 feet in thickness. With the marine sediments, the extended series of volcanic ashes and tuffs is SEMMEt^, GEOLOGY OF THE SAX JUAN DISTRICT 61 intimately associated. The ash beds are usually well bedded aud a cer- tain degree of assortment can be seen in the material that has been either ejected directly into the sea or subsequently reworked. The tuffs are in greater part massive ; others are well bedded and show evidence of marine assortment. The ejectmental material is of all sizes from fine ashes com- posed of grains less than .01 mm. in diameter to coarse tuffs containing fragments a foot or more in diameter. A continuous series is formed between these two extremes^ so that the distinction between ashes and tuffs is merely an arbitrary one based on size of grain. The complexity of the older series is primarily due to large number of igneous rocks tliat occur closely associated with the sediments. But for the fact that the older series has been so thoroughly dissected by igneous intrusions, its correlation and geologic mapping would be a comparatively simple matter. As it is, however, correct mapping can only be done after detailed study of areas where outcrops are numerous. RESIDUAL SOIL AND DEPTH OF DECAY ^N'one of the rock formations of the district is free from surface altera- tion and decay. The older series, longer exposed to the weathering agen- cies, has been altered to considerable depths and is now almost everywhere covered by a residual soil locally reaching many feet in thickness. Its greatest development is in the inner lowland, where the relief is moderate and stream transportation slower. In this region it is often possible to make excavations of 15 feet in depth w^ithout encountering bed-rock. ( ^(msequently, in this lowland region outcrops are uncommon and the few that occur are often so highly decomposed that tlie exact nature of the original rock remains uncertain. Even in the mountainous region where outcrops are plentiful many of them are badly decomposed. The stream beds and recent road cuts afford the best opportunities for the study of extended surfaces of fresh rock. Even though the temperature changes are small, exfoliation is common, producing peculiar concentric arrangements that are strikingly prominent in many of the shales, vol- canics, and igneous rocks (Fig. 10). One of the most striking characteristics of the topography of the old- land is the remarkable stability of the soil mantle. As has already been noted, the soil mantle, remaining practically in situ, might well be re- garded as an important factor in determining the regularity of the crest line, in many places giving rise to well rounded hill summits that have been regarded as good evidences of peneplanation. Hillsides that slope as steeply as 40° can be cultivated with little or no loss of soil. Knife- edge divides with 40° slopes on either side retain their soil to the very st'il'X'flFll' srm'HY ,t raij). lierki-y asrribe^; ilif i-anM'^ ul: ilio htahiliiy of tlif <.til iiarill)' f(. thi'i'c fiiclors { liM-"), p. .i:*) : Jir^^t, th.; dciisc .;'!.\(>r nl" icgctH- itiii: scH'und. the small rarigo in daily ani' aiinuiil tcMujK'nitiirc : and. hird. ihi! low (•(.ntent of itiort; ui- rpl'iiu'tury iiuiloiaal. .-ludi as <|i,iailz. jii In- rutd^s wlinse do>frurtinii \\m fjinii^hi-d the mW. Nciilipr ui: the liist w., of tJieso rart«.rs wnuhl oxplaan tht- <1alHlity of tlio noil w\w\\ iini.ru^- ertfd, >tdi«><|iir'jit. t(> indiivalioii. 'rhc third, however, is, id: vjlal siuniii^^ aiH;»\ The io-n,Mai> Tif ion, roiitaiii large a.moinils d' iVldspars and .■rr.MHci.u-nrsiaii ndnerals, and little or iw quaii.z. 'I1ii< on weatla-riri- voidd -ive rise to an aroillaeeous >oil, essi-ntiallT a elay. whieh would, hv ■ery nii|.ervi,)iB. X veil of this eliaraelTT wnidd not perinit i.he rr«'e «'ii^^. Hth of Bui eiilatioii of ui-oniid waler and woidd tiol readlijy he rcmou'd, and iraiis- jiorted bv {he siirfact! riin^ulT. 'IMie preseiice^ of a^ widespread mantle ed' sueli impervious sod, lui.uiit well explain the peeuliar atwnee of meleorje sprin.u's throudioui the i.hriid. True sprin.H's are atmost uid