[dowling] eastern BELT OF THE CANADIAN CORDILLERAS 177 



British Columbia, somewhat younger than the early Cretaceous 

 sediments of the area but pre-Tertiary in age, may have been contem- 

 poraneous with earth movement which at the close of the Kootenay 

 period changed the outline of the Cretaceous seas east of the old land 

 barrier and may also have been contemporaneous with other move- 

 ments later referred to 



In mid-Cretaceous time the Cretaceous sea was expelled for a 

 short period from the géosynclinal region but entered again from the 

 south and attained greater width than before, but apparently did 

 not connect with an encroaching sea which extended a short distance 

 southward from the Arctic coast. During this period of expansion 

 of the seas and accompanying subsidence of the basins, any stresses 

 due to an adjustment of load would probably produce tension in 

 the crust along the margin of the depressions and compression in 

 the basin areas. That is, normal faulting would probably occur, 

 especially along the western side of the greatest depressions. 



If there is a genetic relation between deep depressions and nearby 

 great elevations as is argued for in the case of the Indo-Ganges trough 

 and the Himalayas, then the Selkirk massif may be considered as 

 directly related to the former great geosyncline which persisted to 

 the east through all of Cretaceous time. The existence of this basin, 

 now modified by the general uplift and upturn of its western edge 

 accomplished in Tertiary time, has been fully proved by information 

 obtained from exposed sections and drilling records. Its present form 

 is illustrated in Figure No. 1 based on a figure reproduced in Memoir 

 116 of the Geological Survey. This figure shows that the deep part of 

 the basin is now close to or even within the present mountains. 

 That the present deepest parts of the basins approximately correspond 

 with the original deepest parts may be deduced from the known 

 thicknesses of the different formations and the way in which these 

 thicknesses vary. The contours of the basin as it now exists, suggest 

 that a governing line existed which helped to maintain the parallelism 

 of the outer mountains. This governing line, it is thought, owed its 

 origin to the existence, as already suggested, of tension with accom- 

 panying normal faulting in the crust at the western edge of the 

 subsiding basin. The great amount of this subsidence near 

 the western land, it is thought, would result in the rising during 

 Cretaceous time along the western margin of the subsiding area 

 of a fault block fronting a former fractured land mass and pre- 

 senting to the sea a wall comparable to that of the coast of Labrador. 

 The presence of this block east of the older land area is disclosed by 

 the areal distribution of the geological formations, which shows that 



12— D 



