IS 



University of California Publications. [Geology 



dimensions normal and parallel to c about equal. It shows a 

 leaching to a green variety, and a further change to chlorite and 

 black specks of iron oxide. 



The ferro-magnesian mineral agrees very well with augite. 

 It is nearly colorless and practically free from pleochroism. A 

 section nearly normal to the prism, oo P (110), shows a cleavage 

 angle of about 90°, and the extinction bisects this angle. There 

 is an alteration of the mineral to a green pleochroic one, possess- 

 ing an absorption color of yellow-green which has some of the 

 properties of epidote ; the alteration, however, is incipient. 

 Green hornblende is also present. It seems in some instances to 

 have been derived from augite. The plagioclase feldspar shows 

 no alteration to caleite, but contains kaolin. No properly ori- 

 entated sections were found in which to measure extinction 

 angles of the lamellar twinning. Orthoclase distinguishable by 

 lowest relief and birefringence and freedom from lamellar twin- 

 ning is present. Qiiartz with irregidar cracks, and possessing' 

 gas and liquid inclusions, is of similar importance. Some apa- 

 tite, 0.8 mm long, is present. This rock may accordingly be 

 designated an augite granite. Another similar rock is 172, 

 which occurs east of it in the Blue Jay Butte. The similarity 

 of the two is marked. The biotite is less altered and the rock on 

 the whole is fresher. In the pyroxene, in sections showing a very 

 pronounced prismatic cleavage, there appears a fine lamellar 

 cleavage which is somewhat discontinuous yet pronounced, and 

 cutting across the coarser at a considerable angle. This lamellar 

 cleavage is basal, and indicates the species diopside. An extinc- 

 tion with the coarse cleavage was obtained in one case as large 

 as 32° on a section parallel to c. The prismatic cleavage is 

 straight and well defined. The alteration of the pyroxene is the 

 same as in slide 123. It shows apparent incipient change to a 

 green pleochroic hornblende. In one instance where the pyrox- 

 ene is surrounded by a considerable border of hornblende, iron 

 oxide is traced along their contact, the hornblende itself being 

 free from it. Biotite includes quartz and pyroxene. In regard 

 to the latter, it occurs both as inclusions and intergrowths, and 

 their relation is such in either case as to indicate that the period 

 of crystallization of the biotite continued beyond that of the 

 pyroxene. The feldspar is the same as is usually seen in granitic 



