224 



DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



to gabbros. The quartz often bears many fluid inclusions. Chlorite, epidote, 

 leueoxene, and a little ealcite are rare secondary minerals. 



Professor Dittrich has analyzed a specimen of the fresh sill-rock from a 

 point situated about nine miles east of the Moyie river and 1-5 miles north of 

 the Boundary line. This specimen (No. 1153) represents the principal rock 

 type of most of the sills. The analysis resulted as follows : — 



Analysis of dominant gabhroid type in the Purtiell sills. 



Mol. 



Si0 2 



Ti0 2 



A1 2 0', 



Fe 2 0., 



FeO 



MnO 



MgO 



CaO 



Na 2 



K 2 



H 2 at 110°C. . 

 H 2 above 110°C. 



P 2 B 



CO, 



Sp. gr (corrected value) 



51-92 



865 



•83 



010 



14-13 



137 



2-97 



019 



6-92 



0% 



•14 



001 



8-22 



205 



11-53 



205 



1-38 



023 



•47 



005 



•10 





1-07 





•04 





•06 





99-78 

 2-990 



A fairly accurate optical determination of the -weight percentages among 

 the principal mineral constituents (Rosiwal method) gave the result: 



Hornblende. 

 Labradorite. 

 Quartz. 



Titanite and magnetite. 



Biotite 



Apatite 



58-7 



34-8 



4-0 



1-4 



•9 



•2 



1000 



The comparative poverty in alumina and the high acidity are evidently 

 related to the composition of the hornblende, which has been estimated as 

 above. In some respects the analysis recalls the diorites but both the magnesia 

 and lime, as well as the amount of femic material in the rock, are too high for 

 that class. It seems best, for the present, to place this type among the horn- 

 blende gabbros, although it is to be regarded as an abnormal variety in that 

 class. 



The standard mineral composition or ' norm ' of the Norm classification 

 was calculated to be : — 



