PETROLOGY 311 



I. Felsophyre from Monterey Mountain, Highland County, Virginia. Darton 

 and Keith, American Journal of Science, 1898, vol. vi, p. 307. 



la. Molecular ratios from I. 



II. Trachyte ( ?) from Robbins Branch, Pikes Peak, Colorado. W. Cross, 

 Bulletin 148, U. S. Geological Survey, 1897, p. 163. 



III. Granite-porphyry from Wolf Butte, Little Belt Mountains, Montana. 

 L. V. Pirsson, Twentieth Annual Report U. S. Geological Survey, 1900, part iii, 

 p. 499. 



The norm, as computed from the analysis in column I, and the position 

 of the Virginia rock in the quantitative system are as follows : 



Norm Ratios 



Q 22.50] • Sal 94.43 



Or 27.80| Class, = — = — — = 19.7 = I, persalane. 



Ab 37.73 |*94.43 * em 480 



An 5.28 ^ a Q 22.50 , . 



C 1.12 Order, — = —— ==0.31 = 4, britannare. 



1 70.81 



Hy 1.53] 



Mt 2.32 



II 0.61 



, OA ^ K 2 + Na 2 122 



h 4.80 Rang, ' ' = — = 6.42= (1)2, toscanase. 



CaO 19 



&::::: °ifr __._. ^ «> 



Subrang, — — - = — = 0.69 = 3 / ', toscanose. 



100.24 



Symbol Name 



I. 4. (1)2. 3'. Liparose-Toscanose. 



QUARTZ-GABBRO (TONALOSE ( ?) ) 



Megascopic character. — Only a single occurrence of this type has been 

 noted in the region. It is found as a single dike, 70 feet wide, in inti- 

 mate association with the complementary series of dikes of nepheline 

 syenite, teschenite (analcite- basalt), and camptonite, occurring in the 

 northern part of Augusta County. The dike of quartz-gabbro crosses 

 the public road on the Arey farm 1.5 miles south of Milnesville, and 

 can be traced along a north 55° west direction for several hundred yards 

 through the fields on either side of the road. Twenty-five feet south of 

 the quartz-gabbro dike is a parallel one of camptonite not exceeding LO 

 feet in width, and which can be traced for a somewhat greater distance. 



The quartz-gabbro is a dark bluish-gray, medium to fine even-granular 

 (granitoid) rock, which weathers to yellowish brown in color. Both 

 feldspar and quartz are readily distinguishable in hand specimens, with 

 the former greatly in excess. Certain phases of the rock exhibit areas a 

 few inches in diameter in which quartz is apparently equal to or greater 

 in amount than feldspar. The quartz is usually of a bluish opalescenl 

 appearance. In addition to the Pelsic minerals, quartz and feldspar, 

 hand specimens are dotted with pseudomorphs after pyroxene of from 

 2 to 3 millimeters in diameter. Thev are bluish-black in color and some 



