GEOLOGY AND GEOLOGIC HISTORY. 55 



of coarse conglomerate. A short distance downstream from the trail an 

 outcrop of this conglomerate forms a bluff 20 meters high along the stream. 

 This rock is similar to the basal Miocene conglomerate exposed along Rio 

 Mao at Bulla. At the last crossing of the trail over Arroyo Clavijo there 

 is an outcrop of basalt that shows rude bedding and resembles the basalt 

 interbedded with limestone of Cretaceous age in the hills south of Gurabo. 

 West of this locality similar flows and pyroclastics crop out most of the 

 way to Sabaneta. About 11 kilometers east of Sabaneta (station 10275; 

 list of fossils given below) tuff is interbedded with a thin layer of bluish 

 limestone conglomerate, the pebbles of which contain poorly preserved 

 fossils similar to those found in the limestone south of Gurabo. 



The fossils collected at stations 10274 and 10275 were submitted to Dr. 

 T. W. Stanton, whose report is as follows: 



Although most of the small fragments of limestone show sections of fragmentary 

 fossils on weathered surfaces none of the fossils could be freed from the matrix by the 

 ordinary methods of preparation. It was therefore necessary to depend on the study 

 of sections as shown on weatheied surfaces and en the polished surfaces of eleven 

 selected specimens, which were ground down and polished. 



Station 10274 (D. C. 68). Limestone about 1.5 kilometers south of Gurabo village 

 near Monci6n : 



Coral. Undetermined genus. 



Radiolites sp. Fragment showing shell structure similar to R. nicholasi Whitfield. 

 Station 10275 (D. C. 69). About 11 kilometeis east of Sabaneta, on telegraph line 

 to Guaraguanca; limestone interbedded with tuff: 

 Coral. Undetermined genus. 

 Radiolites sp. Fragments with some shell structure as in specimen from station 



10274. 

 Caprinula (?) sp. Three fragments of a rudistid with shell structure like that of 



Caprinula. 

 Gastropod. Section of small, slender shell of undetermined genus. 

 The fragments of Radiolites and Caprinula (?) give conclusive proof of the Cretaceous 

 age of the rocks in which they are found, and they suggest correlation with the fossil- 

 ifeious Cretaceous rocks of Jamaica, Cuba, and the Virgin Islands. 



Near Sabaneta there are extensive level plains consisting of sand and 

 gravel that are only slightly cemented. In some of the ravines there are out- 

 crops of the volcanic tuff above described. A broad bench at an altitude 

 of 225 meters is cut by deep ravines here and the»-e. The rocks exposed in 

 the ravines are coarse sand and conglomerate interbedded with clay shale 

 locally containing lignitic bands. 



Other outcrops of volcanic rocks similar to those associated with the 

 Cretaceous limestone near Gurabo and probably of the same age were found 

 south of Sabaneta. Similar rocks outcrop about 5 kilometers south of 

 Sabaneta. A short distance to the south are foothills, which rise to an 

 altitude of about 450 meters. The rocks composing them are of several 

 igneous and metamorphic types, but have been so much weathered that 



