330 DEPARTMENT OF THE INTERIOR 



i 



2 GEORGE V, A. 1912 



Col. 2. First, an amount of Fe 2 3 representing sufficient Fe to satisfy the sulphur 

 present, was apportioned. The sulphides of iron were arbitrarily considered as 

 half pyrite and half pyrrhotite. The remaining Fe,0 3 was calculated to repre- 

 sent the FeO and Fe 2 3 of this rock by assuming that these oxides occur in the 

 average proportions which they have in other analyzed Rossland lavas (Nos. 456 

 and 543). The analysis, so recalculated, is entered in Col. 2; the corresponding 

 molecular proportions are shown in Col. 2a. 



The norm was calculated from the values given in Cols. 2 and 2a, with result 

 as follows : — 



Orthoclase 23-91 



Albite 23-06 



Nephelite 5-40 



Anorthite 15-85 



Diopside .. 19-71 



Olivine 3-09 



Ilmenite 1-52 



Magnetite 2-78 



Apatite -31 



Pyrite and pyrrhotite 2-31 



H 2 and C0 2 1-86 



99-80 



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

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

 germanare. 



According to the older classification the rock is both mineralogically and 

 chemically a hornblende-augite latite. It was nowhere seen to be vesicular but, 

 on account of its persistent fine grain, it is believed to belong to a massive flow 

 rather than to an intrusive body. 



A somewhat similar porphyritic rock, perhaps intrusive, crops out on the 

 Dewdney trail where it crosses the low ridge between Sophie mountain and 

 (the western) Sheep creek. Orthoclase is very abundant in the ground-mass of 

 this rock. 



Hornblende-biotite Latite. — A fifth type of latite was collected on the moun- 

 tain spur running up from Bitter creek southeastward at a point four miles due 

 east of the railroad station at Cascade. The rock crops out at the 3,300-foot 

 contour as a massive, gray to greenish gray, porphyritic, non-vesicular trap, and 

 seems to extend uninterruptedly along the ridge to the 4,300-foot contour, where 

 it is interbedded with hard bands of fine basic ash. Continuing southeastward 

 to the Boundary line, the same lava is seen interbedded with coarse quartz con- 

 glomerate. This type of lava was not identified at any other locality. 



The phenocrysts are brown biotite and green hornblende, the former pre- 

 dominating. The determinable feldspar, averaging labradorite, Ah, An.,, is 

 confined to the ground-mass where it forms minute, tabular, twinned crystals in 

 great number. A green shreddy biotite of low absorptive power and evidently 

 of different composition from the phenocrystic mica, is extensively developed 

 among the plagioclase microlites. This green biotite also forms complete pseudo- 

 morphs after the hornblende phenocrysts, so that it is doubtful that any of the 

 mica of the ground-mass is original. Orthoclase was not observed and jt is 



