174 GEOLOGICAL RECONNAISSANCE OF THE DOMINICAN REPUBLIC. 



eral strike of the beds is northeast and the dip is southeast at an angle less 

 than 25°. These rocks are exposed from Monte Cristi to a place 23.75 

 kilometers east of Monte Cristi, where younger unconsolidated sand and 

 gravel are encountered. 



In the vicinity of Barranca Blanca, in the Monte Cristi Range, sand- 

 stone, sandy calcareous clays and soft white limestone are exposed in the 

 arroyos. The beds are more disturbed here than in other areas of Miocene 

 rocks, although the sediments are less consolidated. The strike shifts 

 from north to east and the dip ranges from 15° to 60°. 



In addition to the beds described in the above paragraph the Miocene 

 series includes a younger group of less consolidated sand and gravel. Such 

 beds are exposed along the road from Monte Cristi to Santiago east of a 

 place 23.75 kilometers from Monte Cristi. Although local dips as high as 

 10° were observed the beds are almost horizontal. The road to Guayubin 

 and Sabaneta branches off the main road 24 kilometers from Monte Cristi. 

 At La Plata, 27 kilometers from Monte Cristi, the fossil marine mollusks 

 listed on page 154 (station 8778) were found partly embedded in the yellow 

 soil that covers the plain. As the shells are numerous and widely spread 

 they seem to be in place. They indicate a horizon high in the Miocene, 

 probably higher than any of the horizons in the Yaque group of the middle 

 Yaque Valley. 



Fossils of the same species were collected at La Subida de la Salina, on 

 the trail through the Monte Cristi Range (station 8777, p. 154). Soft, friable 

 reddish-brown sandstone, which contains the fossils, is exposed along a 

 steep slope almost 60 meters high. The beds strike N. 35° W. and dip 

 30° SE. At the top of the slope is a level plain, above which rise a few 

 rounded hills. On the flank of one of the hills, west of the trail, there is a 

 shallow syncline in reddish-brown sandstone. 



Several low hills near La Barca, on the south side of Rio Yaque, are com- 

 posed of undisturbed coralliferous limestone and sand. The corals (see 

 list on p. 154, station 8780) represent a horizon high in the Miocene, per- 

 haps equivalent to the horizon of the Mao Adentro limestone of the upper 

 Yaque Valley. 



The town of Copey, which stands between Monte Cristi and Dajabon, is 

 built on rather soft, indistinctly bedded coralliferous light-gray sand and 

 clay, which are well exposed immediately south of the town along the road 

 to Dajabon (station 8779, p. 154). These deposits are apparently of 

 Miocene age but may be younger. 



Farther north, on the south side of Rio Yaque between La Barca and 

 Cano de Botijuela, several hummocks that rise above the plain are com- 

 posed of horizontal beds of coralliferous limestone and subordinate amounts 

 of detritus from the limestone. The patches of limestone clearly are coral 

 reefs, which are probably of the same age as the coralliferous deposits at 



