222 GEOLOGICAL RECONNAISSANCE OF THE DOMINICAN REPUBLIC. 



The limestone along this coast is at least in part Eocene, as indicated by 

 Nummulites and other Foraminifera found near the sea beach on the south 

 side of Rio Cana (station 8576; for list of fossils see p. 106). The only fossils 

 found at El Derrumbado were a few fragments of shells and some corals, 

 probably of Eocene age. 



The basalt is evidently extrusive, for it is vesicular and its structure 

 indicates flowage, but some of it is very compact and finely crystalline. 

 The bed of Rio Bahoruco contains boulders of more coarsely crystalline 

 rocks, almost of gabbroid appearance, which may have been derived from 

 an igneous mass farther inland. 



Copper stains are common in the basaltic lava, especially in its vesicular 

 part, where thin films of chalcocite fill irregular cracks that traverse the 

 mass and occur also as impregnations of the tufflike part. The amygdular 

 spaces are generally filled with zeolite materials. At Bahoruco the con- 

 spicuous green malachite stain in the weathered rock has attracted the 

 attention of local prospectors, who have dug trenches and pits over a con- 

 siderable part of the hillside and have done sufficient work to show the 

 futility of further search in this vicinity. Chalcocite occurs in insignificant 

 amounts in the body of the rock and in films, 1 to 3 centimeters thick, 

 that follow irregular, widely separated cracks in the rock. 



Specimens from other prospect pits, farther south along the coast, 

 near Paradis, indicate the occurrence of similar copper deposits there. 

 The owner of the prospect near Paradis reports that his locality is the 

 more promising of the two. One specimen found near Paradis showed a 

 vein, about 5 centimeters thick, composed in part of chalcocite. 



So far as known these are the only places in the Bahoruco Mountains 

 where prospecting has been done for copper. On the strength of these 

 discoveries the concession "Bahoruco" was obtained from the Dominican 

 Government. 



AZUA AND VICINITY. 

 Outline of Geology. 



The town of Azua lies on a gravelly plain that slopes southeastward 

 toward Ocoa Bay. A short distance to the north there are low hills of 

 conglomeratic sandstone and shale, of Miocene age, beyond which lie 

 mountainous slopes of early Tertiary limestone. In the foothills at a 

 place known as Higuerito there is a seepage of oil that has been the 

 chief center of interest for the oil prospectors in the Republic. The fertile 

 plain south of Azua consists of sand and gravel, which is possibly in part 

 contemporaneous with the Las Matas formation of the region to the west. 

 The strata found in drilling for artesian water to a depth of about 100 me- 

 ters at the Ansonia sugar plantation are said to consist of unconsolidated 

 clay, sand, and gravel. Between the plain and the coast to the south is 



