104 GEOLOGICAL RECONNAISSANCE OF THE DOMINICAN REPUBLIC. 



remains of species of corals that are still living. By referring to page 82 it 

 will be seen that this coralliferous limestone is crossed by streams whose 

 lower stretches have been slightly submerged and that there may have been 

 slight emergence after the submergence. These events indicate a consider- 

 able lapse of time after the limestone was formed and would appear to 

 justify its reference to the Pleistocene series. 



Other possible evidence of the age of this limestone may also be con- 

 sidered. Most geologists who have studied the subject hold that during 

 the existence of the continental ice caps the sea level was lowered in the 

 tropics because so much water was locked up in the glaciers. After the 

 glaciers melted the sea level was raised by the return of the water to the 

 ocean. It is therefore at least probable that the drowning of the mouths of 

 the valleys that cross the limestone containing species still living was due 

 to water returned to the ocean by the melting of the Wisconsin ice sheet. 

 The limestone may therefore be of Pleistocene age. 1 



The considerations thus presented apply particularly to the elevated 

 coral-reef limestone of the District of Macoris and the Province of Santo 

 Domingo. Parts of the "coast limestone" may be later than Pleistocene. 

 (For a discussion of the phenomena around Enriquillo Basin see page 77.) 



EXTINCT MAMMALS OF THE DOMINICAN REPUBLIC. 



No mammalian remains were collected during the geologic reconnaissance 

 but as such remains have a bearing on the geologic history of the West 

 Indies it may be noted that G. S. Miller, Jr., has recorded 2 the rodents 

 Isolobodon portoricensis Allen, Plagiodontia aedium F. Cuvier, and Bro- 

 tomys voratus Miller, from collections made in kitchen middens at San 

 Pedro de Macoris by Dr. Theodor de Booy and at San Lorenzo by Dr. W. L. 

 Abbott. The geologic significance of these animals becomes obvious when 

 they are considered in connection with the faunas of Cuba, Porto Rico, 

 and other West Indian islands. Miller says, regarding the West Indian 

 hystricine rodents: 



They suggest direct descent from such a part of a general South American fauna, 

 probably not less ancient than that of the Miocene, as might have been isolated by a 

 splitting off of the Archipelago from the mainland. Of later influence from the continent 

 there is no trace. 



In subsequent field work in the Republic it is highly important that In- 

 dian dwelling sites and caves should be thoroughly explored for vertebrate 

 remains in order to increase our knowledge of the extinct mammals. 



1 For a discussion of West Indian shore-line features, see Vaughan, T. W., Fossil corals from Central 

 America, Cuba, and Porto Rico, with an account of the American Tertiary, Pleistocene, and Recent coral 

 reefs: U. S. Nat. Mus. Bull. 103, pp. 189-524, pis. 68-152, 1919, especially pp. 263-306. 



* Bones of mammals from Indian sites in Cuba and Santo Domingo: Smithsonian Misc. Coll., vol. 66, 

 No. 12, pp. 10. 1 pi., 1916. 



