158 



These intrusions must have been accompanied by some 

 deformation of the Shuswap series. In any case, the plut- 

 onic invasion was followed by erosion which bit deeply 

 into the new terrane — a process long continued, implying 

 great uplift above baselevel. The uplift was, however, 

 not accomplished as an incident of intense folding. The 

 average dip of the Shuswap rocks is today low. It must 

 have been lower in pre-Beltian time, for the planes of 

 schistosity and sill-contacts of the Shuswap are nearly 

 parallel to the basal beds of the Beltian system at Albert 

 Canyon and have been upturned to angles of 45 to 55 since 

 Beltian time. The pre-Beltian deformation may well 

 have developed a broad geanticline accidented by slightly 

 tilted fault-blocks. Their average strike possibly corres- 

 ponded with the present dominant strike of the terrane, 

 namely, about N. 70 E. 



The first sediments formed by the erosion of the Shuswap 

 terrane have nowhere been identified. A great mass of 

 it had already been removed before the region about Albert 

 Canyon was depressed below sea and was covered by the 

 lowest exposed bed of the Beltian system. That bed was a 

 little-washed arkose sand, in mineralogical composition 

 differing but little from the shell of secular weathering on 

 the Shuswap orthogneiss beneath. It is probable that 

 this unconformity represents the preliminary erosion of 

 the Shuswap bedded series at this locality. 



With the geanticlinal uplift of the pre-Beltian terrane, 

 the oldest known structure visibly paralleling the existing 

 Cordilleran axis was developed. The zone roughly repre- 

 sented by the Western Geosynclinal Belt now became a 

 land mass and the zone represented by a large part of the 

 existing Eastern Belt become an elongated basin of deposit- 

 ion (largely, if not wholly, marine in our section). The 

 floor of the basin slowly subsided and upon it the Rocky 

 Mountain Geosynclinal was accumulated. More or less 

 continuously, from the beginning of the Beltian to the close 

 of the Mississippian, this prism increased in thickness; 

 during the Middle Cambrian it was greatly widened by 

 marine transgression far to the eastward, if not to the west- 

 ward, of the initial shore-lines. Detailed study of the 

 sediments shows that their clastic materials, even as far 

 east as the Front range of the Rockies, were largely de- 

 rived from the land on the west, though a small proportion 



