86 GEOLOGICAL RECONNAISSANCE OF THE DOMINICAN REPUBLIC. 



Specimens of dike rocks. 



LAVAS. 



Among the lavas, as among the granular intrusives, there are no decidedly 

 silicic or alkalic types, but there are intermediate, basic, and ultrabasic 

 types. 



Andesites. — A gray poryphyritic typical hornblende-augite andesite 

 was found in the Province of Azua (D. C. 74), and two other specimens, of 

 which no thin sections are available, from the same province, apparently 

 belong to hornblende andesite. A black augite andesite with phenocrysts 

 of plagioclase and augite was collected in the Province of Santo Domingo. 



Basalts. — The collection contains specimens of basalt from the provinces 

 of Monte Cristi, La Vega, Azua, Barahona, and Santo Domingo, and also 

 two specimens from the Departement du Nord, Republic of Haiti. The 

 rocks are variously altered, the olivine in many of them being replaced by 

 chlorite or serpentine. Two extremely fresh specimens of very basic lava 

 classifiable as limburgite rather than basalt are D. C. 76 and 79. One of 

 these contains no feldspar, though feldspar might be present if the glass of 

 the groundmass were crystallized. 



