234 DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



details. The foregoing- description of the usual gabbro will suffice, also, for 

 most of the femic rock in these Moyie sills. 



Yet microscopic and chemical study of the lower internal zone of contact 

 of sill E, shows that here the rock is not quite the same as the usual gabbro. 

 This Phase 7 was collected at a point 30 feet perpendicularly from the lower 

 surface of contact. In macroscopic appearance and internal structure it is 

 not markedly different from the usual gabbro. The essential minerals are horn- 

 blende and labradorite; the accessories, quartz, potash feldspar, titanite, mag- 

 netite. Zoisite, kaolin, and much chlorite are the secondary constituents. 



Chemical analysis of Phase 7 (specimen No. 1143) by Prof. Dittrich gave 

 the following result : — 



Analysis of Gabbro (Phase 7) of Moyie Sills. 



Mol. 



SiQ 2 52-94 -882 



Ti0 2 .73 -009 



A1 2 8 14-22 -139 



Fe 2 3 2-08 -013 



FeO 8-11 -113 



MnO -35 -005 



MgO 6-99 -175 



CaO 10-92 -195 



Na^O 1-40 -023 



K 2 -49 -005 



H 2 at 110°C ; -12 



H 2 above 110°C 1-56 



P-A -08 -001 



99-99 



Sp.gr 2-980 



The corresponding mineral composition in weight percentages is roughly 

 as follows: 



Hornblende 54-8 



Labradorite 25-6 



Chlorite 11-0 



Quartz 6-3 



Titanite 2-0 



Magnetite <>. '3 



100-0 



On account of some alteration in the rock, it was found difficult to dis 

 tinguish with certainty the small amount of alkaline feldspar; which has, 

 accordingly, been entered in the total for labradorite. 



