ORBICULAR GABBRO-DIORITE 



297 



The field relations between, and the mineral composition of, the 

 diorite and granite suggest different periods of intrusion of the two 

 rocks, in the Carolina locality. Close by and approximately parallel- 

 ing the general direction in strike (northeast-southwest) of the orbic- 

 ular gabbro-diorite are some half-dozen dikes of massive unaltered 



Fig. I. 



normal diabase which penetrate the porphyritic granite. While 

 conclusive evidence is lacking, it is not improbable that the orbicular 

 diorite and the neighboring dikes of diabase are of the same age. 

 Southwestward a short distance from the knoll of exposed masses of 

 the typical orbicular structure, the rock loses its characteristic nodular 

 or spheroidal structure and assumes a pronounced granitic texture 

 of rather coarse grain, but composed of the same minerals and of the 

 same general dark color. 



The color of the orbicular rock is dark, with a greenish tint 

 imparted by the dark green ferromagnesian minerals. As indicated 



