University of California . 



[Vol. 3. 



A Bather Basic Fades of tlie Prevailing Granite of Kern 

 Canon. — A medium-grained rock of uniform texture, possessing 

 the normal granitoid habit. Under the microscope it is seen to 

 be composed of plagioelase, orthoelase, quartz, biotite and horn- 

 blende, with accessory magnetite and apatite. The plagioelase 

 occurs in broad plates consisting of closely crowded albite 

 lamellae. Pericline twinning is developed to but slight extent. 

 Incipient kaolinization has rendered the feldspar dull and turbid. 

 The maximum extinction angle measured against symmetric 

 lamella? was 30°, fixing this feldspar as an acid labradorite. It 

 forms the most prominent constituent, comprising nearly half 

 the bulk of the rock. Hornblende and biotite occur as inclu- 

 sions. The orthoelase is developed both in Carlsbad twins and 

 as polysomatie aggregates. Feldspars showing albite twinning 

 have been enclosed by the orthoelase. Zonary banding is rarely 

 exhibited. The quartz is present in allotriomorphic patches and 

 in very subsidiary proportions. Apatite needles occur sparingly 

 among the inclusions. The biotite constitutes the most abun- 

 dant ferro-magnesian mineral present. It shows the character- 

 istic frayed edges and some bending of the plates. The amount 

 of brown-green hornblende is relatively small, but exhibits the 

 strongest approximation to an idiomorphic development. 



The composition of the rock accordingly leads it to be classi- 

 fied as a hornblende-biotite grano-diorite. Some evidences of a 

 cataclastic structure can lie adduced from the curvilinear deforma- 

 tion of the albite lamellae with a tendency to rupture in the more 

 acute flexures. 



Uralitir Gabbro. — This is a coarse grained rock consisting, so 

 far as can be determined in hand specimens, of feldspar and a 

 dark green, ferro-magnesian mineral. In thin section it appears 

 as an allotriomorphic granular aggregate of plagioelase and 

 hornblende, with large amounts of accessory magnetite. The 

 feldspar occurs in broad plates and patches; the twinning 

 lamellae are broad and yield 36° as the maximum symmetrical 

 extinction angle. This would determine the feldspar as labra- 

 dorite. The hornblende and plagioelase are present in nearly 

 equal proportions. The hornblende is light green and has the 

 characteristics of a uralitic derivation. The prismatic cleavage 



