140 PROCEEDINGS OF THE PALEONTOLOGICAL SOCIETY 



upper terraces are found Area tuberculosa, Lucina tigrina, and Turbo pica. 

 On the 10-foot level large numbers of these fossils are found in the lime, sand, 

 and silt which coats this terrace. 



8. East of Guanica, one-eighth of a mile, on the east side of the Susua Valley, 

 a terrace at an elevation of 50 feet contains in the surface material the forms 

 Lucina jamaicensis, Area Uiberculosa, and Turbo pica. 



9. At the town of Ensenada (Central Guanica), the pre-Tertiary is trun- 

 cated and a deposit of shells, muds, silt, and sand covers the surface to a maxi- 

 mum depth of 5 feet. The fossils occur at an elevation of 45 feet and include 

 the following: Murex elongatus, Isophyllia sp., Venus cancellata, Operculum of 

 Turbo, Area rhombea, Cerifhium iHteratum, Ostrea virginica, and Byssoarca 

 ziebra. 



10. On the south side of Pardas Bay, south of Ensenada, the Tertiary lime- 

 stone is again terraced, its elevation being 65 to 100 feet, and the fossils Area 

 rhombea, Area tuberculosa, and Lucina jamaicensis are found buried in the 

 surface soil. 



11. On Cape Rojo, in the southwest corner of Porto Rico, the San Juan for- 

 mation, which has been interpreted by Doctor Berkey as a limesand of dune 

 origin, is found at an elevation of 75 feet overlain by 3 feet of conglomerate 

 consisting of well rounded pebbles. In the San Juan formation occurs a Conus 

 very close to the recent form Con us porto-ricanus. 



12. On Aguilla Point, the extreme southwestern portion of the island, recent 

 gastropod shells are found in consolidated gravels at an elevation of 11 feet. 

 At an elevation of 25 feet they occur on the beveled surfaces of the rocks which 

 make up this point. 



13. Three and three-quarters miles southwest of Mayaguez, on the coast near 

 the reform school, a terrace is cut on the pre-Tertiary rocks at an elevation of 

 50 feet. The inner margin is marked by cliffing, and the following fossils are 

 found in the surface soil : Area tuberculosa, Venus cancellata, and Lucina 

 jamaicensis. 



The argument has been advanced by Mr. Lobeck that where recent fossils 

 have been found in Porto Rico they are associated with Indian mounds. Such 

 an interpretation, however, could not explain the existence of recent shells 

 buried in stratified material of estuarian character at depths of from 2 to 5 

 feet. Furthermore, although in each of the 13 localities cited above the writer 

 made careful search for artifacts, in no instance was evidence found to sub- 

 stantiate the Indian mound theory. 



Based on the evidence presented in the 13 above-mentioned cases, the writer 

 draws the following conclusions : With the recent changes of level of land and 

 sea the old river valleys were embayed, allowing the sea to enter with its 

 marine fauna and to lay down deposits of sand, silt, and mud. That these 

 deposits (for example, localities No, 1, 2, 3, 4, 5, 8, and 9) were laid down 

 in Quaternary time is evidenced by the fact that over 95 per cent of the fossils 

 are of the same species as those living at the present time in the adjacent sea. 



In the remaining instances (6, 7, 10, 11, 12, 13) the truncation of the under- 

 lying beds of limestone and other formations along the south and west coasts 

 and the presence of cliffing at the inner margins of some of these terraces, to- 

 gether with the recent fossils found on the surface, are facts hard to explain 

 if they are not in some way connected with the work of the sea. 



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