GEOLOGY AND WATER RESOURCES NEAR MONTE CRISTI. 171 



outliers about 6 kilometers distant from the main mountains, are a series 

 of rather low hills that trend parallel to the main mountains. The hills 

 south of Copey, which are the northwestern extension of the Cerros de 

 Jacuba, are rounded and less elongate. 



GEOLOGY. 



The following geologic subdivisions have been recognized in the area : 



Recent alluvium. 

 Pleistocene (?) beach deposits. 



Pliocene (?) gravel. 

 Miocene sedimentary rocks. 

 Oligocene tuffs. 



Oligocene (?) limestone and sandstone. 

 Quartz diorite. 



QUARTZ DIORITE. 



During a trip from Sabaneta to Restauracion * by D. D. Condit and 

 the writer quartz diorite was observed at one locality in the foothills of 

 the Cordillera Central. A hill about 60 meters high, called Juan Calvo, 

 which stands about 5 kilometers south of Dajabon, is composed of gray, 

 rather coarsely crystalline biotite-hornblende-quartz diorite, which is 

 cut by small dikes of an aplitic rock and numerous small quartz veins. 

 On the north side of the hill the quartz diorite is sheared along a narrow 

 zone 3 to 6 meters wide. This shear zone strikes N. 40° E. and dips 45° SE. 

 Along the shear zone micaceous minerals are more abundant than in the 

 unsheared parts of the rock. Similar rock probably forms the main mass 

 of the northern part of the Cordillera Central in this area. The age of 

 the rock is not known. 



OLIGOCENE (?) LIMESTONE AND SANDSTONE. 



Hard, compact limestone, probably of upper Oligocene age, was seen in 

 the Monte Cristi Range and in the region immediately north of Dajabon. 

 A low hill about 25 kilometers northeast of Monte Cristi and immediately 

 east of the rope-fiber factory, on the seacoast, is composed of hard, mas- 

 sive cream-colored limestone. The Foraminifera Amphistegina sp., 

 Globigerina sp., and Heterosteginoides ? sp., probably of upper Oligocene 

 age, were collected at this locality (station 8853) . Less than 3.5 kilometers 

 east of this hill similar limestone shows distinct bedding planes that strike 

 east and dip 60° N. Similar limestone was observed at another locality 

 in the Monte Cristi Range on the trail 5.5 to 7 kilometers northeast of the 

 settlement called Isabel de los Torres. The limestone at this place is 

 hard, fine-grained, gray to cream-colored and distinctly bedded. The 

 strike is east and the dip is 60° N. Apparently the limestone has been 

 metamorphosed by the intrusion of small dikes of a hard black aphanitio 

 rock. 



1 See p. 52 of this report. 



