STRATIGRAPHIC PALEONTOLOGY. 103 



sections and as some of them represent mixed faunas adequate strati- 

 graphic knowledge of the Yaque group in the southwest part of the Republic 

 can be obtained only through additional field work. It seems, however, 

 that the principal formations of the Cibao Valley are represented by con- 

 temporaneous deposits on the south side. 



CERROS DE SAL FORMATION. 



Only corals and mollusks are listed from the Cerros de Sal formation. The 

 corals do not indicate the precise position of the formation in the Miocene 

 series, but the mollusks may afford ground for a more definite opinion. The 

 molluscan f aunules at the four localities at which collections were made have 

 only a few species in common and most of these species are pelecypods. 

 The collection from station 8591 is remarkable for the large proportion of 

 pelecypods, which outnumber the gastropods by 100 per cent. The fauna 

 is evidently younger than any of the faunas of the Yaque group on both the 

 north and south sides of the island, for it includes a larger number of Recent 

 species or Recent specific stocks, especially among the pelecypods. 



The formation can not yet be definitely correlated with European di- 

 visions, but if the correlations suggested for the older subdivisions of the 

 Dominican Miocene are correct it should be Tortonian or younger, perhaps 

 Sarmatian or Pontian. 



MIOCENE OR PLIOCENE IN DISTRICT OF SAMANA. 



The plants and fresh or brackish water Mollusca collected at Sanchez 

 (stations 8607, 8764, 8684, and 8685) include the largest collection of fossil 

 plants made during the reconnaissance. The stratigraphic significance of 

 these plants is not yet known, but the beds in which they were found are 

 greatly deformed, so that considerable earth movement has occurred since 

 their deposition. 



PLEISTOCENE OR YOUNGER. 



Nearly all the Pleistocene or later corals and mollusks listed on pages 

 166-168 are now living in West Indian waters, and the few species that seem 

 to be new may yet be found there. The close of Pleistocene time in North 

 America, according to geologic opinion, was marked by the retreat of the 

 last Wisconsin ice cap, between 10,000 and 30,000 years ago, but as the 

 tropics were not directly affected by glaciation it is not always possible to 

 distinguish between tropical Pleistocene and Recent deposits, for at least 

 the marine faunas of the two epochs are almost identical. The reference of 

 a marine deposit within the tropics to the Pleistocene must therefore de- 

 pend upon indirect evidence derived from a study of geologic history, and 

 as the geology of the Dominican Republic has been studied merely in a re- 

 connaisance way only rather general statements as to the deposits of these 

 ages are now warranted. Along much of the southern lowland of the Re- 

 public Miocene limestone is overlain by coralliferous limestone containing 



