157 



in Vancouver Island; by Dawson, Bowen, Camsell, Le Roy, 

 Bancroft and Daly in the Coast range ; and by Daly in the 

 Belt of Interior Plateaus. Their conclusions agree with 

 many recent results of study in the Alaskan and United 

 States portions of the Western Belt. 



GENERAL HISTORY. 



The earliest event demonstrated in the rocks of our sect- 

 tion is the long-continued erosion of a silicious( granitic or 

 gneissic) land surface older than the Shuswap series. No 

 actual representation of this ancient mass has been dis- 

 covered, but its existence is inferred from the abundant 

 development of clastic, sandy and argillaceous beds of 

 Shuswap age in south-central British Columbia. This 

 deposition continued long, though it was often interrupted 

 by the precipitation of limestone (e.g., Sicamous formation.) 

 Clastic and chemical sediments together formed a geosyn- 

 clinal mass several kilometres in thickness. Within it 

 there is no sign of unconformity. Toward the close of this 

 epoch of sedimentation and before any notable deformation 

 of the geosyncline, basic lavas broke through the earth's 

 crust and buried the older deposits very deeply (Adams 

 Lake greenstone). 



The lower members of the series were drastically affected 

 by static metamorphism, whereby sediments and lavas 

 became converted into true crystalline schists — metargill- 

 ites, phyllites, and other mica schists, quartz-sericite 

 schists, calc-schists, chloritic and uralitic schists. Exces- 

 sive fissility essentially parallel to bedding-planes was thus 

 imposed upon the Shuswap series. It was then invaded by 

 granitic magma which sent off-shoots into the easily split 

 schists, in the form of innumerable sills, laccoliths, and 

 dykes, on a scale seldom matched. The plutonic invasion 

 took place by successive stages, so that older intrusions 

 are cut by younger. As so often the case, the youngest 

 magmas were aplitic or pegmatitic in habit. This salic 

 material forms countless small bodies in the Shuswap 

 terrane. Practically all these intrusions, except the 

 youngest aplites and pegmatites, were themselves sub- 

 jected to static metamorphism, converting them into 

 orthogneisses. The resulting schistosity, generally well 

 developed, is sensibly parallel to the stratification planes of 

 the adjacent sediments. 



