326 DEPARTMENT OF THE INTERIOR 



2 GEORGE V, A. 1912 



The calculated norm is : — 



Orthoclase 32-25 



Albite 26-20 



Nephelite 1-42 



Anorthite.. 17-79 



Diopside 6-87 



Olivine 10-18 



Ilmenite 1-82 



Magnetite 1-62 



Apatite 1-24 j 



Water , -60 



9999 i 



According to the Norm classification the rock enters the sodipotassic sub- 

 Tang, monzonose, of the domalkalic rang, monzonase, in the dosalane order, 

 germanare. The mineralogical and chemical composition and structure all 

 perfectly match the typical augite latite of Table mountain, California, as 

 originally described by Ransome.* The analysis of the more basic phase of the 

 Table mountain flow is entered in Col. 2 of the foregoing table. 



From the fresh rock just described all transitions to profoundly altered 

 phases are represented in the area. The latite. has often been transformed into 

 a dark green, massive rock, still showing its porphyritic character by the presence 

 of broken and altered feldspar phenocrysts or of uralitic pseudomorphs after the 

 augite. For the rest the completely changed rock is, in thin section, seen to be 

 a confused mass of epidote, calcite, quartz, chalcedony, chlorite, biotite, uralitic 

 and actinolitic amphibole, zoisite, pyrite, etc., in ever varying proportion. Some- 

 times, though not often, an amygdaloidal structure is preserved. This is not so 

 much because it has been obliterated by metamorphism as because these lavas 

 were largely non-vesicular when first consolidated. 



Augite-biotite Latite. — This type of massive lava is at least as important in 

 the area as the augite latite. As above noted, the two varieties grade into each 

 •other, and the only noteworthy persistent difference is the absence or presence of 

 biotite among the original phenocrysts. Biotite also often occurs in minute, 

 shreddy foils in the ground-mass but it appears to be generally of secondary 

 origin. The phenocrystic biotite is of a deep, rich brown colour and has powerful 

 absorption; its optical angle is probably under 2°. The other phenocrysts, the 

 accessories, and the ground-mass have characters essentially identical with those 

 of the augite latite. 



No perfectly fresh specimen of the augite-biotite latite was secured. One of 

 the least altered ones, collected on the ridge joining Record and Sophie moun- 

 tains, at a point two miles north of the Dewdney trail (No. 456), has been 

 analyzed by Mr. Connor. It is a compact, deep greenish-gray rock with numerous 

 small phenocrysts of labradorite (averaging about Ab 1 An 2 ), biotite, and urali- 

 tized augite. These minerals are embedded in an abundant, originally 

 hyalopilitic, greenish base. The latter is chiefly devitrified glass. Its advanced 



* F. L. Raneome, American Journal of Science, Ser. iv. Vol. 5, 1898, p. 359. 



