Vol. 4] Knopf-Thelen. — Geology of Mineral King. 



251 



ular groups of minute tourmaline prisms are of comparatively 

 frequent occurrence in the groundmass. 



A section cut from a hand specimen taken from near the 

 intrusive granite showed somewhat surprising' features. The 

 quartz porphyry at the contact is standing on edge and does 

 not differ macroscopieally from the previously described facies, 

 which was taken from altitude 8,300, Little Kern trail. The 

 microscope shows that the porphyritic quartzes have retained 

 their integrity and idiomorphic habit in nearly perfect preser- 

 vation. They display strong undulose extinction, and may occa- 

 sionally be fractured to small extent, but rarely show traces 

 of granulation. The ferromagnesian minerals are conspicuously 

 absent from the quartz porphyries. 



The tuff associated with these acid volcanics does not differ 

 greatly from them in its physical aspect. It is, however, more 

 massive, and does not contain numerous porphyritic quartzes. 

 Included in it are dark lenticular patches, representing frag- 

 ments of extraneous origin. Under the microscope only a few 

 irregular fragments of quartz are apparent, and these are af- 

 fected by strain shadows. Phenocrysts of orthoclase are more 

 numerous, and frequently retain their idiomorphic habit, Some 

 are fractured, and the fragments, especially the corners broken 

 off from the phenocrysts, show cross-hatched twinning. A few 

 of the larger feldspars display the microcline structure in 

 splendid perfection. The delicate cross-hatching is on a fine 

 scale, and has been developed uniformly over the area of the 

 feldspars. The plagioclases are less abundant than the potash 

 feldspar and have been somewhat capriciously affected by the 

 dynamic metamorphism. Some still show the re-entrant twin- 

 ning angles; others are peripherally granulated; and a lath was 

 found broken into three pieces and the fragments separated. 



Phenocrysts are not abundant, and the ferromagnesian min- 

 erals are nearly absent, A few small strips of biotite were 

 found, as were some irregular patches which appear to represent 

 localizations of flaky biotite. The ground is cryptocrystalline, 

 and contains scattered through it very minute scales of biotite. 

 Some magnetite, a few zircons showing perfect terminations, and 

 some small prisms of tourmaline occur as accessories. 



