COETEZ AND PAPPOOSE PEAK EEGIOK 577. 



southwest direction, and about 3 miles in width, which rises quite abrunlly 

 4,000 feet from the plain. It is cut through by two sharp canons, which ex- 

 pose its structure very clearly. It presents singularly few dividing planes, 

 and is remarkably solid, unbroken, and unseamed. It is composed of two 

 feldspars, both entirely undecomposed, one of salmon-colored orthoclase, 

 the other, a slender, white, triclinic feldspar, with quartz, which appears to 

 be both translucent and of a milky whiteness, large white crystals of color- 

 less orthoclase, long prisms of dark-green hornblende, and considerable bio- 

 tite. There are not unfrequent veins and passages of granite, where all the 

 constituents appear very large, the orthoclase reaching an inch and a half, 

 and the quartz an inch in extent. The hornblende is here gathered into 

 confused bunches of needles ; and there is present a second mica, probably 

 muscovite. The quartz contains fluid-inclusions: magnetic iron in small 

 quantity and a little apatite are also present. The rock presents every 

 variety of texture, from large pegmatite occurrences down to a fine, com- 

 pact, salmon-colored mass, in which all the ingredients are too fine to be 

 detected by the naked eye, the rock having a felsitic appearance, clouded 

 here and there by a mere dusting of very fine hornblende and mica. 



An analysis of a medium-grained variety of this granite was made by 

 Prof. Thomas M. Drown, with the following result : 



Silica 72.01 



Alumina 14.75 



Ferrous oxide 2.35 



Manganous oxide 0.17 



Lime 0.79 



Magnesia 0.65 



Soda 4.21 



Potassa 4.49 



Ignition 0.61 



100.03 



CoRTEz AND Pappoose Peak Region.^ — Directly to the south of this 

 granite mass, and occupying the bold heights of Cortez Peak and the hill- 



'Froui field-notes of Clarence King. 

 37 D G 



