184 GEOLOGICAL RECONNAISSANCE OF THE DOMINICAN REPUBLIC. 



line of some parts of the mountains suggests the presence of undisturbed 

 sedimentary rocks that are younger than the rocks of the basal complex. 

 The flat-topped hills west of Sabana de la Mai , south of the western part 

 of the bay, are principally or entirely underlain by massive pink to white 

 limestone, which is apparently almost horizontal. Although the limestone 

 is fossiliferous no determinable fossils were found in it during the recon- 

 naissance. As has already been suggested (p. 64), this limestone may be 

 an eastward extension of the limestone that overlies the Cevicos limestone, 

 but additional studies are needed to determine the geologic age and rela- 

 tions of these limestones. 



MIOCENE OR PLIOCENE CLAY, SAND, AND CONGLOMERATE. 



Barely consolidated sands and clays underlie the low, rolling country 

 that borders the mountains between Sanchez and Rancho Espanol. Some 

 of the clays contain so much organic matter that they resemble lignite. 

 A[bed of lignitic clay 2.5 meters thick was examined near Punta de Santa 

 Paula. A bed 35 centimeters thick, which contains a higher percentage of 

 organic matter, is exposed near the warehouse at Sanchez. None of the 

 beds of lignitic clay examined, however, have any value as fuel. The 

 sands, which are interbedded with the clays, are for the most part fine- 

 grained but locally contain pebbles. 



Although these beds are only slightly disturbed they are folded and 

 faulted at some places, where the dips may be as steep as 45°. Many 

 small folds and a few normal faults of slight displacement are exposed 

 along the shore between Sanchez and Punta de Santa Paula. The beds 

 strike generally N. 50°-60° W. and except in the disturbed areas dip gently 

 toward the southwest. The terrace flats described on page 181 bevel the 

 deformed strata of this formation. 



The fossil coastal plants and brackish water mollusks that were col- 

 lected from clays of this deposit near Sanchez (see lists on p. 165, stations 

 8607, 8764, 8684, and 8685) are probably of Miocene or Pliocene age. 



The heavy coarse conglomerate that forms the islands and much of the 

 steep parts of the shore near Samana is probably of the same age. The 

 pebbles composing this conglomerate comprise metamorphosed limestone, 

 limestone conglomerate, and different kinds of igneous rocks, embedded in 

 a soft calcareous matrix. 



The marly coralliferous limestone in the vicinity of Los Rosales and 

 Rancho Espanol and the oyster-bearing limestone bed near Punta Gorda 

 may also be of the same age. 



PLEISTOCENE OR RECENT TERRACES AND CORAL REEFS. 



The presence of terrace flats whose surfaces bevel the plant-bearing 

 clays and sands at and near Sanchez has already been mentioned (p. 184). 

 The terraces are probably of Pleistocene age. 



