PETROGRAPHY OF PLUTONIC ROCKS 197 



slides, but this mineral was present in a section from another specimen 

 of a similar granodiorite found not far from the locality of number 10, 

 thus showing the presence of titanium in the magma from which num- 

 ber 10 was probably crystallized. 



A. M. S. number 12, from Pine flats, appears to be a normal grano- 

 diorite, although it appears to be high in MnO and low in MgO. It 

 contains traces of titanium and phosphoric acid, although not in as 

 large quantities as do most of the Sierra Nevada rocks of the same class. 



Hornblendite. — Hornblende-gabbro is found quite abundantly through- 

 out the range, occurring generally as large irregular dikes or masses 

 associated with the more acid rocks. A typical occurrence is in Rubio 

 canyon, at the foot of the famous Mount Lowe railroad incline. The 

 rock at this locality is nearly pure hornblende. Another characteristic 

 hornblendite is found on the slopes of mount Waterman, on the divide 

 between the east branch of Buckhorn canyon and Bear canyon. Speci- 

 mens (A. M. S. number 24) from this area show slight alteration, are 

 rather fine grained and greenish hued, and consist principally of horn- 

 blende. Plagioclase feldspar, in crystals much smaller than those of the 

 hornblende, also occurs sparingly in the rock. In thin sections the 

 most important constituent is seen to be the large crystals of hornblende, 

 which show bluish green to yellowish green pleochroism. Calcite is the 

 principal alteration product of the hornblende, and often replaces a large 

 percentage of the original mineral in some of the crystals. Small num- 

 bers of considerably altered plagioclases fill the interstices between the 

 hornblende crystals, and, in some instances, form inclusions in the latter. 

 Epidote in small grains is an occasional constituent. A chemical anal- 

 ysis of this rock (A. M. S. number 24) from mount Waterman, by A. M. 

 Strong, gives the following results : 



Si0 2 49.68 



A1 2 3 12.07 



Fe 2 U 3 10.57* 



MnO Trace 



CaO 13.85 



MgO . 9.02 



K 2 1.15 



Na 2 3.31 



H 2 56 



100.21 



A piece of water-worn hornblendite from Tujunga canyon below the 

 mouth of Alder creek is almost black in color, and in the hand specimens 

 shows nothing but large crystals of hornblende. In thin-sections this 



*FeO determined with Fe 2 3 . 



