76 GEOLOGICAL RECONNAISSANCE OF THE DOMINICAN REPUBLIC. 



MIOCENE OR PLIOCENE SERIES. 

 Plant-Bearing Beds at Sanchez. 



Beginning at an exposure about 180 meters east of the pier at Sanchez, 

 unconsolidated plant-bearing clay and sand containing seams of limonite 

 crop out for several kilometers eastward along the south shore of Samana 

 Bay. In the exposure 180 meters east of the pier (station 8684) the strata 

 dip eastward at an angle of 24°; 270 meters east of the pier (station 8685) 

 they dip westward at an angle of 45°. At other localities farther east they 

 show diversity in both strike and dip. More detail on this formation is 

 given on page 184, and fossils from it are listed on page 165. The data at 

 hand are inadequate for fixing the geologic age of the deposit, but as it is 

 older than the terraces that bevel its surface around Sanchez it is tenta- 

 tively referred to the Miocene or Pliocene. 



PLIOCENE SERIES. 

 Las Matas Formation. 



The name Las Matas formation is applied by Condit and Ross (p. 201 of 

 this report) to loosely consolidated deposits of gravel, clay, and limestone in 

 the valley of San Juan and adjacent areas. The name is taken from the 

 village of Las Matas, in the province of Azua. The Las Matas formation 

 lies unconformably upon the Yaque group. The contact is plainly shown 

 at a place on Rio Yaque del Sur 3 kilometers upstream from Los Guiros, 

 where the Yaque group is overlain with angular unconformity by the Las 

 Matas formation. At this locality the strikes as well as the dips are dis- 

 cordant. 



The formation consists chiefly of gravel but includes some marly lime- 

 stone and clay. The gravel is yellowish-gray and is less firmly cemented 

 than the conglomerate of the Yaque group. The clay is faint reddish to 

 purplish, presenting a marked contrast to the bluish-gray to olive-green clay 

 of the Yaque group. The formation looks like a subaerial deposit. The 

 gravels resemble outwash material such as is now being laid down along 

 the border of the mountains in this region. 



No fossils have been found in the Las Matas formation, but it is evidently 

 younger than the Miocene, and as it is certainly older than some deposits 

 referred to the Pleistocene it is provisionally regarded as Pliocene, though 

 it may be early Pleistocene. 



QUATERNARY SYSTEM. 



Raised coral reefs that are evidently not older than Pleistocene were seen 

 at almost every place along the shore that was visited by members of the 

 expedition, and the coast charts show raised reefs at many other places. 



Adjoining the living reef that partly encloses the harbor of Puerto Plata 

 is a dead reef, now standing 2.5 to 3 meters above sea level. At San Pedro 

 de Macoris fossil reefs are even more conspicuous. The flat, rocky plain 



