l8 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 30 Ser. 



c being green, 6 yellowish brown, and a pale yellow-green 

 to almost colorless. The absorption formula is c > & > a. 

 Inclusions are not common and are principally magnetite. 

 There is an occasional intergrowth with biotite. The alter- 

 ation of the hornblende is well advanced in many of the 

 slides. It appears to be undergoing a uralitic change by 

 which it is transformed into a dirty greenish, fibrous aggre- 

 gate, much like "reedy hornblende," with a rather weak 

 pleochroism. This secondary hornblende has usually a 

 parallel arrangement of its fibres, and the terminals of the 

 sections are generally more or less ragged. It also occurs 

 in finely fibrous, irregular areas, with the fibres irregularly 

 oriented. A further alteration of the hornblende is mainly 

 into chlorite and calcite. 



Biotite is not common, though occasionally found. The 

 sections are strongly pleochroic, always show irregular 

 boundaries, and the mineral occurs either alone or inter- 

 grown with hornblende. The biotite is in part altered to 

 chlorite, and some of its sections are wholly surrounded by 

 a chloritic margin. No inclusions occur, except occasional 

 grains of magnetite. 



Augite is present in some of the slides, being variable in 

 amount, but at times forming an important constituent. It 

 generally presents very irregular boundaries, but several 

 sections were seen showing roughly the crystal form charac- 

 teristic of cross-sections of augite. It has a granular, much 

 broken appearance, and a high refractive index. Its most 

 characteristic feature is a clouding of the area by an opaque, 

 dirty-brown decomposition product. Few of the sections 

 were free from this product, and it marked the mineral 

 wherever found. The augite is practically colorless, and 

 is without any sensible pleochroism. No cleavage was 

 observed anywhere, and only one case of twinning. Where- 

 ever the augite comes in contact with the hornblende the 

 boundary line is sharp and clear. When it occurs in isolated 

 sections these are usually free from the uralitic product 

 described in connection with the hornblende. This, 

 together with the freedom of all the hornblende areas from 



