GEOLOGY AND GEOLOGIC HISTORY. 77 



which there forms the point between the harbor and the ocean is a 

 reef that stands about 2.5 meters above the sea. This plain is composed 

 of hard, nodular, white or yellowish limestone containing many living 

 species of corals. Doctor Vaughan recognized near or at the sea front the 

 corals Orbicella annularis, Maeandra strigosa, Manicina gyrosa, Siderastrea 

 siderea, Acropora muricata, and Acropora palmata. Back from the shore 

 this hard rock merges laterally into soft, creamy-yellow nodular limestone. 

 A cut near the steamer dock at Macoris exposes about 3 meters of this 

 marl, in which there are many corals representing species characteristic of 

 protected but clear water. The following species were identified by Doctor 



Vaughan : 



Orbicella annularis (Ell. and Soil.). 



Maeandra labyrinthiformis (Linn.). 



Manicina gyrosa (Ell. and Sol.). 



Agaricia agaricites (Linn.). 



Siderastrea siderea (Ell. and Sol.). 



Acropora muricata (Linn.). (Most abundant species.) 



Porites porites Lam. 



Porites astreoides Lam. 



At Santo Domingo City the sea front in the vicinity of the wreck of the 

 U. S. S. Memphis is bordered by a raised reef. 



Lake Enriquillo is bordered by a terrace of coral limestone at an altitude 

 of about 35 meters above sea level and about 79 meters above the present 

 level of Lake Enriquillo. This coral reef is conspicuous at Neiba and 

 Duverge, but farther east it takes the form of a flat-lying bedded limestone. 

 It is either of the same age as the conglomeratic "coast limestone," which 

 extends from Cabral southeastward beyond Barahona, or it is a little 

 younger. Plate XVII, B (p. 198), is a view of a part of this reef. 



The "coast limestone," which was referred to the Pleistocene by Gabb, 

 is not a unit but includes sediments ranging in age from Miocene to Recent. 

 Much of it, however, is of Pleistocene age. A large part of it is soft, pul- 

 verulent, marly limestone, which is locally called "caliche." Some of this 

 rock is conglomeratic and contains large boulders of older rocks of many 

 kinds. 



Raised rocky beaches, which still carry clinging shells, such as Mytilus, 

 were seen at several widely separated places, notably several kilometers 

 inland from San Pedro de Macoris, at an altitude of more than 30 meters 

 above sea level, and along the shore northeast of Monte Cristi. 



The fossils collected from Pleistocene or younger deposits are listed on 

 pages 166-168. 



STRUCTURE. 



The structure of the Dominican Republic as a whole is simple, but its 

 details are very intricate. The oldest rocks form a broad strip through the 

 center of the island, and the younger rocks flank them on each side. 



