372 



University of California. 



[Vol. 3. 



much darker than the enclosing- rock, being of a dark pepper- 

 and-salt gray aspect. 



The structure, as seen under the microscope, is that of a hyp- 

 idiomorphic granular aggregate of feldspar, biotite, hornblende, 

 and quartz, with accessory magnetite and apatite. The domi- 

 nant constituent is orthoclase and a small amount of associated 

 plagioclase. It is remarkable for the large number of inclusions 

 contained in it, either arranged centrally or zonally, a sharply 

 defined zone of inclusions being succeeded by a margin of feld- 

 spar showing poor, irregular crystallographie boundaries. The 

 inclusions consist of biotite and magnetite and indeterminate 

 dark, earthy material. The quartz occurs in very sparing pro- 

 portions, and cannot be ranked higher than an accessory. Biotite 

 is the most abundant ferro-magnesian mineral; hornblende is 

 present in subordinate amount. Apatite is notably abundant 

 in small prisms. 



The third specimen is a fragment of a large inclusion over a 

 foot in diameter, contained in a medium coarse biotite granite. 



Microscopically, it is a fine grained gray rock containing 

 numerous hornblende needles. Microscopically, it consists of a 

 hypidiomorphic aggregate of green hornblende, biotite, feldspar, 

 with accessory apatite and magnetite. Orthoclase is the most 

 abundant constituent, forming nearly 75 per cent of the total 

 content. The greater part occurs in allotriomorphic patches, 

 often showing strain shadows. A small amount of acid plagio- 

 clase is also present. Green horublende is the dominant 

 ferro-magnesian mineral, and is noteworthy on account of its 

 strong tendency to develop idiomorphic forms. Biotite occurs in 

 lesser amount in laths and flakes, and as inclusions in the 

 hornblende. 



Lamprophyric Dykes. — Of the numerous small dykes which 

 cut the granite of Kern Canon between the mouth of Coyote 

 Creek and Lower Lake, four have been microscopically examined. 

 Two of these from the multiple dyke a little above the mouth of 

 Coyote Creek prove to be vogesite, while the others from two 

 dykes near Upper Kern Lake are camptonites. 



One specimen of vogesite is a dense greenish gray rock show- 

 ing abundant porphyritic prisms of hornblende. 



