56 GEOLOGICAL RECONNAISSANCE OF THE DOMINICAN REPUBLIC. 



they could not be classified in the time available. Perfect exposures were 

 seen in the gorge of Rio Yaquejal, which was followed for a distance of sev- 

 eral kilometers. Along the lower part of the gorge there are exposures of 

 dark bluish to serpentine green volcanic rock, similar to the basalt east of 

 Sabaneta, but more indurated and containing coarse veins and much epi- 

 dote. The mass has been greatly broken by minor faulting. Intruded into 

 the volcanic rock are irregular dikes of granitic or dioritic porphyry, at least 

 5 meters wide. Farther up the river this volcanic rock lies in contact with a 

 blue sericite schist or phyllite, which also is cut by numerous large irregular 

 dikes similar to those that cut the greenish volcanic rock down the river. 

 It is significant that the volcanic rock of serpentine green color cut by the 

 granitic dikes is similar in appearance to the basalt found east of Sabaneta 

 interbedded with fossiliferous limestone conglomerate of Cretaceous age. 

 Whether these two rocks are of the same age could probably be determined 

 by carefully tracing the outcrops between the two localities. It would be 

 interesting to learn whether the granitic dikes were formed before or after 

 the Cretaceous limestone conglomerate. 



TERTIARY SYSTEM. 



Rocks of Tertiary age occupy probably two-thirds of the area of the 

 Dominican Republic. Lower and perhaps middle Eocene deposits were 

 not seen, but upper Eocene, middle and upper Oligocene, Miocene, and 

 Pliocene deposits have been recognized. The names of the Tertiary for- 

 mations and those of some of then supposed equivalents are shown in the 

 following correlation table : 



