214 GEOLOGICAL RECONNAISSANCE OF THE DOMINICAN REPUBLIC. 



Such faulting appears to have occurred near Lake Rinc6n, where the gyp- 

 sum and salt-bearing beds crop out as ridges in the midst of the valley. 



Vicinity of Barbacoa and Eastward. 



Both Barbacoa and Neiba stand on a terrace of coralliferous limestone 

 that is about 80 meters above the level of Lake Enriquillo. At Barbacoa 

 this terrace, which is only a few hundred meters wide, has a back slope of 

 limestone rubble, which we ascended for more than 2 kilometers without 

 reaching any outcrops. In a deep ravine well up the slope, where cliffs 

 50 meters high are exposed, the rubble is stratified as though waterlain 

 and dips southward at an angle of 15°. The rubble consists entirely of 

 gray semicrystalline limestone containing many orbitoid Foraminifera of 

 Eocene age (station 8595, list of fossils on p. 106). The mountain top in 

 the rear as seen from the valley is made up of limestone. The altitude is 

 estimated at 1,300 meters. Several kilometers west of Barbacoa outcrops 

 of limestone appear to extend down to the shore. The mountain front 

 is probably a fault escarpment and may extend eastward to the vicinity 

 of Boca Mula, on Rio Yaque. 



The rocks exposed in the few outcrops northward from Neiba for a dis- 

 tance of several kilometers show great variation in strike and are steeply 

 inclined. The strata exposed nearer Neiba are probably of the same age 

 as the Cerros de Sal formation on the south side of the basin and are 

 doubtless in fault contact with the pre-Miocene limestone on the north. 

 The results of observations by A. F. Dixon, who made a geological investi- 

 gation in this area, 1 indicate that from Neiba eastward to Rio Yaque 

 the structure is synclinal and that the rocks consist in large part of beds of 

 late Miocene age, which are in places covered by nearly flat strata sup- 

 posed by Mr. Dixon to be the "coast limestone." Elsewhere the "coast 

 limestone" extends up to an altitude of little more than 70 meters above 

 sea level. In this region there are probably also areas of gravels of the Las 

 Matas formation, which elsewhere unconformable overlie the Miocene 

 strata. 



Cerros De Sal. 



The Cerros de Sal were named from beds of rock salt, which are there 

 exploited on a small scale to supply local demand. The rock salt occurs 

 also in the ridge near Las Salinas and for several kilometers westward. 

 The associated gypsmn beds extend eastward along the south side of Lake 

 Rincon and upfaultcd blocks of these beds also appear on the north side of 

 that lake as far east as Rio Yaque. The beds can be traced westward 

 nearly to Duverge. Throughout their extent they generally dip steeply 

 northward but in places they stand vertical or are even slightly overturned. 



The stratigrapbic sequence as studied about 3 kilometers west of Las 

 Salinas, in the vicinity of the Manuel Perez excavations, is shown in the 



1 Report furnished by Mr. R. D. Upham, of the Interocean Oil Co. 



