[GNEOUS ROCKS OF WESTERN ARIZONA. 91 
rock, with quartz and feldspar phenocrysts. Under the microscope 
the texture is porphyritic and dopatic. The phenocrysts are large, 
occasionally somewhat corroded, and the groundmass is xenomorphic- 
holocrystalline. The phenocrysts are orthoclase, greater in amount 
than quartz, and much greater than acid plagioclase. The plagio- 
clase occurs in but few crystals; it has, in part at least, an index of 
refraction less than Canada balsam, and is probably all albite. The 
groundmass is a quartz-feldspar aggregate with much hematite. 
Secondary kaolin and sericite are derived from the feldspar, and the 
red iron oxide perhaps from magnetite. 
ROCK SAMPLES FROM NORTHWESTERN ARIZONA. 
Following is a list of rock samples collected in northwestern 
Arizona with the original specimen numbers: 
A fi. Granitic gneiss from south end of Hualpai Mountains. 
A -10. Granite porphyry from base of Boundary ('one west of Black Mesa. 
A 44. Biotite granite from mouth of Williams River. 
A-49. Granite gneiss from Williams Canyon. 
101. Rhyolite flow breccia from Lost Basin, about 5 miles south of Colorado River, 
in a depression of older crystalline rock. 
A-35. Rhyolite breccia from Temple Bar. 
A-7. Rhyolite from southern end of Black Mesa, at base of cliffs. 
A.— 39. Rhyolitic tuff from ( iolorado River west of Boulder ( Janyon. 
A-12. Rhyolite from Black Mesa, at Gold Roads. 
A L3. Rhyolitic tuff from Black Mesa, in pass east of Gold Roads. 
A-19. Rhyolitic tuff from Black Mesa, at summit of Union Pass. 
A— 43. Rhyolitic tuff from bluffs of Colorado River in Chemehuevis Valley. 
A-2. Hornblende andesite from southern end of Aquarius Mountains, a few miles 
north of Date Creek. 
A-ll. Andesite from Black Mesa, north of Boundary Cone. 
A-40. Andesite from north end of Black Canyon. 
A-41. Andesite from south end of Black Canyon. 
A-42. Andesite from Eagle Rock, near Little Round Island. 
107. Andesite from coyote holes northwest of Kingman, at western edge of mesa. 
A-18. Andesite from a sheet above the rhyolite 2 miles northwest of Kingman. 
110, 111. Basalt from a flow sheet 300 feet thick resting on top of 400 feel of varicolored 
ash and breccia at mouth of White Cliff Creek. 
112. Andesite resting on granite at top of Cottonwood Cliffs near mouth of Cotton- 
wood Creek, 1,200 feet above Nos. 110 and 111. 
A-3. Olivine basalt from a sheet in the detrital beds of Santa Maria Canyon, near 
mouth of Big Sandy Wash. 
A-15. Basalt intruded into the rhyolite 1 mile west of Kingman. 
A Hi. Basall from a flow sheet above the rhyolite 1 mile west of Kingman. 
A 27. Olivine basalt from a sheet above the andesite near Kingman. 
A-30. Olivine basalt from a columnar sheet resting on the Temple Bar conglomerate 
north of Colorado River in Grand Wash. 
A-34. Olivine basalt from a flow sheet within the Temple liar conglomerate near 
Greggs Ferry. 
