220 GEOLOGICAL RECONNAISSANCE OF THE DOMINICAN REPUBLIC. 



are terminated by small cliffs, probably due to wave action in the sea that 

 once filled Enriquillo Basin. 



Along the border of the mountains, yet semi-detached from them, there 

 are foothills, 40 to 100 meters high, composed of clayey sandstone, clays, 

 and conglomerate, and probably some limestone. No fossils were collected 

 from these beds, but it is believed that they form a part of the Cerros 

 de Sal formation, because they are lithologically similar to some of the 

 lower beds of that formation and lie stratigraphically above beds that make 

 up the mass of the higher mountains in the northern part of Sierra Bahoruco. 

 Near Duverge the strike of these beds ranges from east-west to N. 50° W. 

 and the dip ranges from 20° to 50° NE. 



From Duverge southward through Sierra Bahoruco past Puerto Escon- 

 dido to Canada Diablo there is a single series of sedimentary beds. As 

 indicated in the stratigraphic section given on page 215, this series consists 

 of several distinct parts, but there appear to be no great stratigraphic 

 breaks between them. Nearly all the beds are calcareous and most of 

 them are impure limestones. Many are fossiliferous, but the fossils are 

 poorly preserved. There are corals, casts of pelecypods, and some Foramin- 

 ifera. The beds are probably early Miocene or late Oligocene. At their 

 base is a well-defined conglomerate with oval pebbles of hard limestone 

 5 to 6 centimeters and more in diameter. Many of the pebbles contain 

 abundant orbitoidal Foraminifera. 



A striking feature of this region of calcareous rocks is the intensely red 

 color of a very large part of the clayey soil, which is apparently a product 

 of the weathering of the limestone. A thickness of some 130 meters of the 

 rock series is made up of red and yellow highly ferruginous clay-stones, 

 but these are subordinate in amount to the limestone. The red color of the 

 soil is most noticeable where limestone strata form the bed rock. 



The average strike of the beds is N. 70° W., although variations of 10° 

 or more from this were noted. The rocks are folded into open anticlines 

 and synclines, but no considerable faults were observed. Over most of the 

 area between Duverge and Canada Diablo the dips are as high as 60°, 

 but dips of 15° to 25° are more common. Near Canada Diablo and Rancho 

 Viejo, however, there is a change. Here the beds are bent sharply upward. 

 Dips of 70° N. to vertical are common, and at some places, as in the basal 

 beds near Rancho Viejo, steep southerly dips were observed, indicating 

 that the beds here are actually overturned. 



The basal conglomerate containing foraminiferal limestone pebbles is 

 found in the vicinity of Rancho Viejo on both sides of Canada Rancho 

 Viejo, a few kilometers above the point where it joins Canada Diablo. This 

 conglomerate rests directly upon the limestone from which its pebbles are 

 derived. There is clearly an unconformity here, and probably a large one. 

 The limestone is hard, fine-grained, semicrystalline, and massive. No 



