GRANITES OF NORTH CAROLINA 403 



blende, some feldspar and quartz, and may contain much additional 

 pyrite. The rock is a typical amphibolite derived from an original 

 diabase or diorite or both. 



The structural relations of the dikes to each other and to the 

 inclosing granites clearly indicate at least two different periods of 

 penetration of the granites by the basic rocks, and therefore different 

 ages for the dikes. More or less complete evidence of schistose 

 structure in the inclosing granites is sometimes noted in those cases 

 where cut by dikes of similar structure. I take it that the period of 

 intrusion of the dike antedates that of the dynamic disturbance induc- 

 ing schistosity into both dike and granite alike. In those cases 

 where the dike rock remains massive and the inclosing granite shows 

 evidence of schistose structure, the reasonable conclusion is that the 

 basic dike material penetrated the granite after the period of dynamic 

 disturbance closed. 



GRANITE DIKES 



True granite dikes of normal composition and usually fine texture 

 are numerous in certain areas, but only in one or two instances have 

 they been observed penetrating the granite masses. In the main 

 granite belt of the Piedmont region dikes of this character are quite 

 frequent, penetrating the surrounding rocks, and they must be 

 regarded as apophyses from the granite massifs (Fig. 6). As a rule, 

 they vary only a few degrees from the vertical ; are irregular in out- 

 line ; fine-grained in texture ; composed of light to pink feldspar and 

 quartz, with subordinate amount of mica, which may entirely fail at 

 times; and they range from a few inches to several feet in width. 



PEGMATITE AND APLITE. 



Pegmatites are present in large numbers in some quarries and 

 entirely fail in others. As a rule, they do not attain very large size, 

 but are narrow, apparently deep-seated, and of aqueo-igneous origin. 

 Others are limited in extent, surrounded entirely by the granite, 

 marking in such cases true veins of segregation. Texture and com- 

 position of the two are identical. They are chracterized by the usual 

 coarse crystallizations of feldspar and quartz, with subordinate stout, 

 platy, black biotite. The feldspar may be pink or white, showing 



