250 



DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



thick basic sills cutting silicious sediments. More indirect corroboration is 

 offered in certain cases where large basic injections have become differentiated 

 by gravity, apparently after the absorption of considerable limestone. 



QUARTZITE 









llfill 



-v":-7. 



































QUARTZITE 



QUARTZITE 



QUARTZITE 

 QUARTZITE 



QUARTZITE 



Granite 



Acidified 

 t/abbro 



Gabbro 



Figure 16. Diagram illustrating the hypothesis that the partially differentiated 

 syntectic magma of a thick sill may break through the roof and form, 

 at stratigraphically higher horizons, several thinner sills differing in 

 composition among themselves. Some later differentiation in the derived 

 sills is assumed. The original sill is shown in the drawing on the left : 

 the derived sills and the remnant of the original sill are shown in the 

 drawing on the right. The channels (dikes) connecting the sills are not 

 indicated. 



Direct parallels to the Moyie sills have already been noted as occurring 

 in the Purcell range to the east of the Moyie river. Schofield has found many 

 other stratified sills in the same range north of the Boundary belt.* At Sud- 

 bury, Ontario; at Pigeon Point, at Governor's Island, and at Spar, Jarvis, and 

 Victoria islands, and other localities in Minnesota, and among the Logan sills 

 on Lake Superior the same general association of gabbroid-granitic magmas 

 and quartzose sediments occurs. These instances were cited in the writer's 

 1905 paper, where a rather full summary of the facts concerning Pigeon Point 

 and Sudbury intrusives was given. There, and still better in the original 

 memoirs of Bayley, Barlow, and Coleman, the reader will find evidence of the 

 extreme similarity of these cases to that of the Moyie sills. Many other examples 

 have been described in late years, but it is hardly appropriate or necessary to 

 note them individually in the present report. 



* S. J. Schofield, Snmmai'y Report of the Director, Geol. Survey of Canada, 1909, 

 p. 136, and 1910, p. 131. 



