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THOMAS L. WATSON 



county near Hiddenite. Large areas of biotite granite of medium 

 to coarse texture are located in the northern part of the belt. The 

 Mount Airy area in Surry county, near the Virginia line, may be 

 taken as the type. 



LITHOLOGICAL CHARACTERS. 



The Mount Airy granite area. — Quarries are worked one and, a 

 half miles north of the town of Mount Airy, on a ridge slope of con- 

 tinuously exposed granite. In mineral composition the Mount Airy 

 granite does not differ essentially from some of the types already 

 described, though hand specimens of the rock bear little or no resem- 

 blance to each other. The usual granitic minerals are noted, such 

 as quartz, orthoclase, microcline, plagioclase, biotite, muscovite, zir- 

 con, apatite, epidote, chlorite, and magnetite. In addition to these, 

 several grains of allanite have been noted in one of the thin sections. 

 Orthoclase is in excess of the microline in all of the sections examined, 

 accompanied by a larger proportion of finely striated acid plagioclase. 

 Zonal growth and Carlsbad twins are beautifully developed in some 

 of the feldspars. Biotite of brown color and strong pleochroism is 

 the principal accessory, and is altered into chlorite, a colorless mica, 

 and some epidote. Much secondary muscovite derived from the 

 alteration of the feldspar and biotite is present. The large individuals 

 of quartz and feldspar indicate peripheral shattering in finer-grained 

 mosaics of the two minerals filling the interstices. 



GRANITES OF THE APPALACHIAN MOUNTAIN REGION. 

 GENERAL CHARACTERS. 



Areas of granite and granite-gneiss resembling essentially in min- 

 eral composition some of the granite types described above are known 

 over parts of the mountain region of the state. Those of the extreme 

 northwest part of the state have recently been mapped and described 

 by Keith. ^ Since, with perhaps a single exception, those of the 

 other parts of the mountain region are not unlike certain types 

 already described in this paper, only one type is of special interest 

 here, namely, unakite, which occurs in the vicinity of Hot Springs, 



^Geologic Atlas of the United States, 'Cranberry Folio, North Carolina- 

 Tennessee." U. S. Geological Survey, 1903. 



