172 GEOLOGICAL RECONNAISSANCE OF THE DOMINICAN REPUBLIC. 



Several hills north of Dajabon show exposures of hard, gray massive 

 limestone similar in lithology to the rock in the Monte Cristi Range, 

 which contains Foraminifera, probably of upper Oligocene age. 



Immediately north of these hills, on Sabana Canongo along the trail 

 from La Loma to Dajabon, is an outcrop of hard sandstone, which grades 

 into conglomerate. This sandstone contains numerous fragments of the 

 shells of marine mollusks. Although the bedding is indistinct the strike 

 is apparently east and the dip is rather gentle to the north. This sand- 

 stone is considered older than the Miocene sediments because of its greater 

 induration. 



Hard, calcareous sandstone, overlain by conglomerate interbedded with 

 sun-cracked sandstone, was also observed in the Monte Cristi Range east 

 of the rope-fiber factory on the seacoast about 25 kilometers northeast of 

 Monte Cristi. The beds strike N. 65° W. and dip 55° NE. 



OLIGOCENE TUFFS. 



Tuffs were observed at two localities in the Monte Cristi Range. Green 

 weathered tuff outcrops along the coast at an altitude of about 45 meters 

 above sea-level in an arroyo approximately 5 kilometers southeast of the 

 rope-fiber factory. The tuff is not bedded, but a short distance upstream 

 it is interbedded with coarse-grained sandstone, which strikes north and 

 dips eastward. Corals that are apparently of Oligocene age and that are 

 listed on page 111 (station 8775) were collected from thin calcareous beds 

 intercalated in the sandstone. 



Green jointed rock, which is apparently a fine-grained tuff, is exposed 

 at an altitude of about 75 meters above sea level in Arroyo Guanito on the 

 trail to Barranca Blanca, 9 or 10 kilometers from the rope-fiber factory. 

 At this locality the tuff grades upward into a conglomerate composed of 

 pebbles that have a maximum diameter of 15 centimeters. The con- 

 glomerate is overlain by hard, buff-colored, indistinctly bedded limestone. 

 The beds strike N. 60° W. and dip about 70° SW. 



Pebbles of green chloritized tuff and lava are of widespread occurrence 

 in this region and similar tuff and lava were found in place in the Cordillera 

 Central south of Sabaneta. 1 



MIOCENE SEDIMENTARY ROCKS. 



Limestone, sandstone, and shale and less consolidated sand and clay of 

 Miocene age are widely spread in the vicinity of Monte Cristi. Obviously 

 the Miocene series includes several formations, but their relations were not 

 definitely ascertained. The exposures on the slopes of El Morro, near 

 Monte Cristi, indicate that Miocene sedimentary rocks form a large part 

 of the western Monte Cristi Range. Rocks of the same age or slightly 

 younger underlie the entire lower part of the Yaque Valley. 



See p. 52 of this report. 



