GRANITES OF NORTH CAROLINA 2>11 



variable quantity of biotite and, in places, some additional horn- 

 blende as the characterizing accessories. The prevailing large amount 

 of plagioclase feldspar in the rocks is a very noteworthy feature; 

 rarely does this constituent sink to very subordinate proportions, but 

 usually it is almost equal to, or even exceeds in amount, the potash 



Fig. 2. — Granite bowlders on Dunn's Mountain, near Salisbury, North Carolina. 

 Showing weathering along the joint-planes. 



feldspars; and only in a few of the sections studied does it entirely 

 fail. In many of the areas the poverty of the rocks in the ferromag- 

 nesian silicates is a striking feature — a fact well illustrated in the 

 large and important granite area in Rowan county, known as Dunn's 

 Mountain, and its southwestern extension. 



PORPHYRITIC GRANITES. 



In all respects save that of texture the porphyritic granites are 

 identical with the normal granites. They are usually coarser in tex- 

 ture than the even-granular rocks, but mineralogically the two are 



