398 THOMAS L. WATSON 



very likely to the segregation type.^ It does not exist in quantity 

 large enough to be worked over any part of the area traversed by me; 

 hence it has only scientific interest. 



STRUCTURAL FEATURES OF THE GRANITES. 

 MEGASCOPIC STRUCTURES. 



Joints. — ^With possibly one or two exceptions, the CaroKna gran- 

 ites are characterized by a strong development of the jointed structure, 

 the planes of which break the rock into polygonal blocks of different 

 sizes, as indicated in Fig. 4. The most noteworthy exception is that 

 of the extensive granite area near Mount Airy, in which no visible 

 jointing is apparent. Careful measurements of the joint-planes were 

 made in all the granite openings visited in the state, and the results 

 can be summarized as follows: Those joints whose planes lie in the 

 northeast and the northwest quadrants respectively, and composing 

 the major jointing; and two minor sets whose planes strike east- west 

 and north-south. In the northeast and the northwest quadrants the 

 limits of variation in the strike of the joint-planes are N. 10° E. or W., 

 to N. 80° E. or W. Out of the total number of joint-planes meas- 

 ured fifty-six lie in the northeast quadrant and forty-five in the north- 

 west quadrant; while nineteen strike in a north-south direction, as 

 against sixteen having an east-west strike. 



Slickensides . — As a rule, the joint-planes show smooth, more or 

 less polished and striated surfaces, indicating considerable movement 

 in the rocks since the formation of the joints. Strias are developed 

 in a thin coating of yellow to yellowish-green mineral substance, 

 derived from certain minerals in the granite and produced by the 

 rubbing together of the two sides along the plane. 



Schistosity. — Between the perfectly schistose granites (granite- 

 gneisses) and the perfectly massive granites, nearly all gradations in 



I Since this paper was written, Phalen ("A New Occurrence of Unakite," Smith- 

 sonian Miscellaneous Collections, Vol. XLV (1904), pp. 306-16) has published a pre- 

 liminary paper on the occurrence and petrography of unakite at Milams Gap in Virginia. 

 The rock in which the unakite occurs in the Virginia locality is reported by the author 

 to be hypersthene akerite. The epidote of the unakite is secondary, replacing pyrox- 

 ene and feldspar, both plagioclase and orthoclase. The author believes the unakite 

 has originatedLfrom the akerite by hydrometamorphism, aided perhaps by dynamic 

 disturbances- 



