GRANITES OF NORTH CAROLINA 407 



disturbance inducing the schistose structure in the inclosing rocks. 

 Likewise the schistose dikes were intruded at an earher period and 

 prior to the metamorphism of the inclosing rocks, for the field evidence 

 indicates that the schistose structure in the dike and the inclosing 

 rock is the result of the same forces. Until the age of the inclosing 

 rocks is definitely determined, that of the more schistose dikes must 

 largely remain conjectural. As stated, the dikes must antedate the 

 period of pressure-metamorphism affecting the inclosing rocks, for 

 both dike and inclosing rock are similarly affected. 



The sandstones of Triassic age occupying the marginal position 

 along the eastern border of the Piedmont region, are cut by a system 

 of typical massive, unaltered, diabase dikes. The dikes conform, 

 as a rule, to northeast and northwest directions, and are coincident 

 in strike with that of the joints in the sandstones for these directions. 

 Nowhere have the dikes been observed to cut rocks younger than the 

 sandstone, and their age is accordingly definitely fixed as middle 

 -Mesozoic. They are correlated with flows of the same composition 

 and age in New Jersey, New York, and the Connecticut Valley 

 region, and with similar dikes in Virginia and Georgia to the north 

 and south of the Carolina area. 



The dikes of the Carolina sandstone belt are traced into the 

 neighboring crystalline rocks of the Plateau region, where they have 

 wide distribution. Beyond the limits of the sandstone belt, in the 

 crystalline areas penetrated by the dikes, close similarity in texture, 

 structure, and composition of the massive dikes obtains, and their 

 relations to the inclosing crystalline rocks make it reasonably certain 

 that they are of the same age as those penetrating the Triassic sand- 

 stones. 



Thomas L. Watson. 



Geological Laboratory, 

 Denison University. 



