530 T. L. WATSON LITHOLOGICAL CHARACTERS OF VA. GRANITES 



garnet, chlorite, and kaolin. Hornblende is one of the most abundant 

 constituents and at times it completely incloses shreds of the biotite. 

 Microcline does not occur. Plagioclase is probably slightly more abund- 

 ant than orthoclase. Metamorphic effects are indicated in the optical 

 disturbance of the quartz and feldspar ; in fractures crossing the quartz ; 

 in curved and bent lamellae of a part of the plagioclase, and in the marked 

 distortion of the cleavage angle of the hornblende. 



The Annandale type. — This type is a medium gray and medium tex- 

 tured massive biotite-granite, intermediate in texture and color between 

 the Eichmond light gray and dark blue types. It is mineralogically 

 similar to the Eichmond types. Orthoclase is the dominant feldspar. 

 Considerable microcline is present, but plagioclase is less abundant than 

 elsewhere. Quite a sprinkle of idiomorphic sections of garnet is noted. 

 Crushing effects are somewhat strongly marked in the thin-sections in 

 the partial granulation of the quartz and feldspar, with the fine mosaic of 

 the two minerals filling the interspaces of the unmashed portions of these 

 minerals. 



TJndkite. — This type of rock derives its name from the Unaka moun- 

 tains in western North Carolina and eastern Tennessee, where the rock 

 was first observed and described.* Until very recently, knowledge of it 

 was limited to a single locality in Virginia, namely, at Milams gap, in 

 the Blue ridge, near Luray, but it has been noted near Troutdale, in 

 Grayson county, f The mineral composition of the rock from the Virginia 

 and North Carolina-Tennessee localities places it among the granites, with 

 epidote as an essential constituent, but, according to an analysis by 

 Phalent of specimens from Milams gap, the rock is relatively basic for 

 a granite. 



The rock is a moderately coarse but irregular crystallization of red 

 feldspar, quartz, and green epidote. Irregular crystallization of the rock 

 is shown in the variation of masses composed of more than two-thirds of 

 the red feldspar through all gradations to masses composed of quartz and 

 epidote without feldspar, epidosite (see Phalen, page 312). Thin-sections 

 of the unakite from Milams gap show epidote, orthoclase, quartz, iron 

 oxide, zircon, and apatite. The epidote is secondary,^ replacing pyroxene 

 and feldspar, both plagioclase and orthoclase. 



The unakite-bearing rock at Milams gap is, according to Phalen, a 

 hypersthene akerite (hypersthene-quartz-diallage-s}^enite), a coarse grained 

 dark grayish green aggregate of essentially feldspars and black pyroxenes. 



*F. H. Bradley: Am. Jour. Sci., 3d aeries, vol. evii, 1874, pp. 519-520. 



+ Thomas L. Watson : Am. Jour. Sci., vol. xxii, 1906, p. 248. 



% W. C. Phalen : Smithsonian Miscellaneous Collections, vol. xlv, 1904, pp. 306-316. 



§ W. C Phalen : Op. cit. 



