REPORT OF TEE CHIEF ASTRONOMER 



237 



SESSIONAL PAPER No. 25a 



Table XIII. — Showing Columnar Section through the Moyie Sills. 



•Sills, thick- 

 nesses in 

 feet. 



Rock zones, 



thicknesses 



in feet. 



Character of rock. 



Average 



specific 



gravities of 



igneous 



rocks. 

















A, 135 



25 



85 

 25 



Acidified gabbro, 2 specimens, sp. gr. 2 '89 and 2 '97 



2 93 



2'76 







2 '97 











100 















B, 30 



30 





2 99-4- 











550 















80 

 110 



60 

 280 



Biotite granite, 5 specimens, sp. gr. 2 '72 — 2 '754 



2'73 



C, 530 



Hornblende-biotite granite, 3 specimens, sp. gr. 2 '74 — 2 '84.. 

 Intermediate rock, 2 specimens, sp. gr. 2 '95 and 3 00 .... 



2'78 

 2 97 

 300 











75 



Quartzite 













•> 

 950 + 



Hornblende-biotite granite 



2'85 



D, 1050 



Intermediate rock 



Gabbro 



292 

 2 '99 











750- 















50 + 

 150 + 



Intermediate rock . , 



294 



E, 200 + 





297 + 







Quartzite of great thickness 











Sill A is well exposed on the eastern slope of the mountain at the contour 

 300 feet lower than Monument No. 214. The overlying quartzite dips 54° in 

 a northeasterly direction. The uppermost 25-foot zone of this sill is acidified 

 gabbro. That rock shows rapid transition into an underlying, 80-foot zone of 

 biotite granite, which similarly graduates with some rapidity into a nearly 

 quartz-free gabbro approximating the usual rock of the thinner Purcell sills. 

 This is the only one of the sills which has been seen to have a gabbroid zone 

 overlying a granitic one. The upper gabbroid zone seems to represent a layer 

 of magma which was rapidly chilled against the cool roof of quartzite. The 

 lower part of the mass had a longer period of fluidity and became stratified 

 through gravitative differentiation. 



Between sills A and B is a 100-foot layer of quartzite, with strike N. 25° 

 W. and dip 65° E.N.E. 



Sill B, 30 feet thick, is a fine-grained gabbro of the usual type in the 

 Purcell sills; it is apparently of quite homogeneous. composition throughout. 



