GEOLOGY OF THE HAYSTACK STOCK 211 



The norm of B calculated from the analysis is given in column I of 

 the above table. This variety is a little lower in silica, potash, and 

 magnesia than variety A, and richer in alumina, ferrous iron, and lime, 

 while it contains approximately an equal amount of soda and ferric 

 iron. Its mode is given in column II of the above table. According 

 to the quantitative classification it is hartzose and in composition 

 closely resembles a granodiorite from Grass Valley, Nev., described 

 by Mr. W, Lindgren.^ It is also somewhat similar to a granite from 

 Butte, Montana, described by Mr. W. H. Weed.^ 



VARIETY C. TONALOSE: QUARTZ-BEARING DIORITE 



Southwest of the summit of Baboon Mountain and near the outer 

 edge of the stock the rock is fine-grained, dark, and nearly aphanitic, 

 though a few small dark minerals are visible. This rock is cut by 

 small dikes of light-colored medium-grained granite, which are 

 described on p. 223. 



Under the microscope the rock is seen to be holocrystalline, and 

 allotriomorphic granular. The minerals, in order of relative abun- 

 dance are andesine, pyroxene, orthoclase, quartz, biotite, magnetite, 

 and apatite. Andesine, orthoclase, and quartz occur as interlocking 

 anhedra, varying from 0.02 to 0.04"^"^ in diameter and constitut- 

 ing approximately 70 per cent, of the rock. The ferromagnesian 

 minerals are rather evenly spaced with respect to the quartz and 

 feldspar. Pyroxene occurs in bodies from 0.02 to 0.32™°^ in 

 diameter, those of the smaller size being much the more numerous. 

 The smaller bodies approach idiomorphism, while the larger ones 

 are irregular in form. Both augite and hypersthene are present. 

 Biotite is less abundant and occurs as f oliae from o . i to o . 3™"^ long. 

 Magnetite occurs in irregular bodies the size and number of which 

 are something less than those of biotite. Apatite is present as long 

 prisms. The usual order of crystallization was as follows: (i) 

 Magnetite and apatite; (2) Pyroxene, plagioclase, and biotite; 

 (3) Orthoclase and quartz. 



An analysis of C, from a specimen taken near the outer edge 



1 Seventeenth Annual Report, U. S. Geological Survey, Part I, p. 724, 

 1896. 



2 Journal of Geology, Vol. VII, p. 739, 1899. 



