390 THOMAS L. WATSON 



THE MAIN GRANITE BELT. 



GENERAL CHARACTERS. 



This belt is an irregular one in width, occupying the central part 

 of the Carolina Piedmont region, and extending from near the Vir- 

 ginia line in Person county, North Carolina, in a southwest direction 

 across the state into Mecklenburg and Gaston counties, along the 

 South Carolina line. The whole or a part of a dozen counties are 

 included within the limits of this belt. Granite, either massive or 

 schistose in structure, forms the principal rock type over the belt. 



Texturally two distinct phases of the granite are developed, an 

 even-granular and a porphyritic granite, both of which have wide 

 distribution. With the single exception discussed on p. 381, the two 

 texturally unlike rocks represent phases of the same granite mass. 

 In all other essentials the normal and the porphyritic granites are 

 closely similar. 



Over many parts of the belt the granite manifests some evidence of 

 the effects of intense dynamic forces, in many instances resulting in 

 the partial or complete development of a secondary schistose struc- 

 ture. In thin sections of the rock from those areas in which the 

 granite megascopically appears entirely massive, evidence more or 

 less pronounced of pressure-metamorphism is shown. 



The rocks are usually colored some shade of gray, light or dark, 

 in accordance with the proportion of the ferromagnesian mineral 

 present. In some a pronounced pink prevails, and the biotite, which 

 is in very small amount, is not noticeable in the rock. Hardly with- 

 out exception, the rocks are biotite granites, containing in several 

 places additional hornblende, which is the principal accessory in the 

 granite of several areas in Mecklenburg county, although biotite does 

 not entirely fail in these. Muscovite as a primary constituent is 

 sparingly developed, in a few localities, in association with biotite. 



Microscopically the granites are essentially the same in mineral 

 composition as those described above and to the east of this belt. 

 Plagioclase feldspar is a nearly constant constituent, though subject 

 to some variation. At times it exceeds the potash feldspar in amount, 

 and it does not entirely fail in but one or two of the thin sections. 

 Optically it corresponds to a very acid plagioclase, albite or oligo- 

 clase, or both. Orthoclase and microcline are both usually present 



