360 DEPARTMENT OF THE INTERIOR 



2 GEORGE V, A. 1912 



Quartz 5-1 



Sodiferous orthoclase and microper.tbite 51-2 



Andesine, Ab 5 An 3 17-9 



Hornblende..' 20-2 



Augite 1-5 



Magnetite 1-7 



Titanite 1-6 



Apatite and zircon -8 



100-0 



From these proportions the chemical composition of this specimen has been 

 roughly calculated. It is assumed that the hornblende has the same composition 

 as that of the hornblende in the ' quartz-monzonite ' of Mt. Hoffmann, Cal., and 

 that the alkaline feldspars are present in the ratio of two of orthoclase to one 

 of albite. The result is as follows : — 



Si0 2 59-2 



Ti0 2 -7 



A1 2 15-9 



Fe 2 0„' 2-2 



FeO! 2-7 



MgO 2-8 



CaO 4-9 



Na 2 3-6 



K.O 5-8 



H 2 -4 



P 2 5 -4 



Remainder 1-4 



100-0 



The soda is probably too low, yet the calculation seems to show that the 

 analysis made for Mr. Brock would correspond well with that of the typical 

 specimens collected during the Boundary survey. 



The rock is evidently a typical hornblende-biotite pulaskite. Sometimes 

 the biotite is almost or entirely absent, though the composition suffers no other 

 essential change — giving an alkaline hornblende syenite. More rarely, the inter- 

 stitial quartz increases notably and the syenite has the composition and habit 

 of the more acid hornblende-biotite nordmarkite. 



Basic Phase at Contact. — The most notable change in composition is found 

 in a strong basification along the main contact. This was observed at the 

 southern contact along the Dewdney trail, on Record mountain and on the 

 western contact north of Sutherland creek, but the most signal illustration occurs 

 on the northwestern contact near Coryell. In the last locality the railway cut- 

 tings and the high bluffs to the south of the railway track display the basified 

 zone very finely. It is there at least a mile wide and much wider than on the 

 other sides of the batholith. The basic phase appears to merge gradually into 

 the normal pulaskite on the south. The rock is rather dark gray, coarse-grained, 

 and strikingly rich in the femic minerals, hornblende, diopside, and biotite, 

 named in order of decreasing abundance. Andesine, near Ab 5 An 3 , is the pre- 

 vailing feldspar, and accompanies orthoclase and microperthite. The accessories 



