402 



THOMAS L. WATSON 



exposures of the rocks, and hence more or less deeply decayed, while 

 many of them were exposed in the quarry openings, which afford 

 excellent opportunity for observing their relations to certain struc- 

 tural features of the granite discussed below (Fig. 5). In several 

 quarries in widely separated parts of the state a series of some half- 

 dozen or more dikes were observed. Where exposed in the quarries, 



Fig. 5. — Dike of diabase penetrating granite in ttie city of Charlotte granite 

 quarry, North Carohna. Part of a second dike is visible in the extreme left of 

 the view. 



none of the dikes exceed fifty feet across, and usually they are less 

 than four feet. 



Lithologically tw^o types are indicated. The first is usually an 

 unaltered massive diabase, the thin sections of which show under the 

 microscope the essential minerals and structure of diabase. The 

 pyroxene in this type may be considerably altered in some of the dikes, 

 and in hand specimens the rock presents a rather pronounced green- 

 ish hue, resulting from the alteration. The second type is more or 

 less completely thinly schistose, and is largely composed of horn- 



