GEOLOGY OF THE PROVINCES OF BARAHONA AND AZTJA. 207 



Geologic section in vicinity of Quito. Coraza. 



Las Matas formation. Loosely cemented conglomerate, sand- in meters, 

 stone, and variegated clays, with a little marly limestone; color 

 of clays varies from faint maroon to olive green; no fossils seen. 

 These beds rest unconformably on the marine Miocene beds of 

 the Yaque group 150+ 



Yaque group : Sandstone, coarse to conglomeratic, with light olive 

 to gray shaly beds in lower part. Large Areas and other 

 fossils plentiful in the lower beds 600 



Clay-limestone member, with branching corals and layers of 



limestone filled with fossils (station 8590) 200 



Sandstone, conglomeratic 100 



Shale, bluish with thin laminae of sandstone; no fossils seen 400 



Sandstone and conglomerate, bluish sandy shale, and thin, non- 

 persistent beds of limestone ; some of the beds containing a few 

 fossils, chiefly fragments of branching corals and oysters 1500 (?) 



Oligocene and Eocene?. Shales, bluish gray, with thin beds of 



calcareous sandstone 700 



Limestone, gray, sparingly f ossilif erous ; unmeasured; forming the 

 slopes of Martin Garcia. 



The lowest beds recorded in the above section appear along an arroyo 

 that emerges from the hills at the north edge of Quita Coraza. The high- 

 est beds of conglomeratic sandstone of the basal member of the Yaque 

 group form a dip slope of 43°, against which the river waters wash, leaving 

 a precarious footing for travelers along the trail. Perfect exposures of 

 successively lower beds are washed bare in the arroyo, which is dry except 

 during infrequent rainstorms. The rocks consist of an unvarying alterna- 

 tion of even-bedded sandstone and sandy shale with some conglomerate 

 and a few thin, nonpersistent beds of gray limestone. In the conglomerate 

 are embedded a few oysters and broken corals, together with fragments 

 of other shells. Some of the shaly beds contain impressions of leaves and 

 stems of plants. This thick sandy member rests on shale underlain by 

 limestone, which appears far up the arroyo in the steep slopes of Martin 

 Garcia. 



The above described beds of the lower part of the Yaque group resemble 

 sandy strata that appear along Rio Yaque from the crossing of the Azua- 

 San Juan road northward, and it is surmised that the two are equivalent. 

 They are believed to be the basal Miocene beds, and most if not all of the 

 underlying shale and limestone probably is of Oligocene age. 



The next higher member in the section is non-fossiliferous dark-gray 

 shale containing thin laminae of sandstone one-fourth to one-half centimeter 

 thick, spaced at nearly equal intervals of 3 to 4 centimeters in the shale. 

 The thickness of this shale is 140 meters. 



Overlying the dark gray shale are strata that may be designated the 

 clay-limestone member. This member is about 60 meters thick and con- 

 sists of gray, impure limestone and a little sandstone interbedded with 



