242 

 SUMMARY HISTORY. 



There is no record in the Kamloops district of pre- 

 Carboniferous formations, and the area was probably 

 subject to erosion during the early Paleozoic. The Main 

 Pacific Geosyncline was initiated probably in Carboniferous 

 time, and the Cache Creek formations laid down in an 

 eastwardly transgressing sea. Sedimentation was interrupted 

 at times by vulcanism. 



The close of the Paleozoic was marked by deformation 

 and a return to continental conditions. Submergence 

 in Triassic time brought a return of marine conditions, 

 with the deposition of argillaceous and siliceous muds and 

 limestones, accompanied by volcanic activity on a grand 

 scale. Vulcanism ceased in Lower Jurassic time and 

 sedimentation continued with the deposition of arenaceous 

 limestones rich in marine fauna. 



Orogenic movements in the upper Jurassic were either 

 preceded or followed by intrusions of granitic batholiths, 

 stocks and tongues as well as volcanic activity along the 

 east front of the Coast range (Spence's Bridge Volcanic 

 group). 



During the Lower Cretaceous marine conditions were 

 locally restored in geosynclinal downwarps, which received 

 the detritus washed in from the lands, especially from that 

 on the east. Later an emergence took place and these 

 areas seem to have shared in the erosion of the later Cre- 

 taceous. Therewith much of the cover of the Coast 

 Range batholith was removed and the Interior Plateau 

 country was brought down nearly to base level. 



During the Laramide revolution the thick Mesozoic and 

 older formatioms were greatly uplifted, locally folded and 

 overthrust from west to east. The Coast Range and 

 Columbia Mountain systems were loci of maximum uplift, 

 and may have supported local alpine glaciers. 



The Laramide revolution invigorated the drainage and 

 made the rivers deeply entrench themselves within the 

 older Cretaceous erosion surface. The Coldwater group 

 conglomerates, sandstones and shales were then deposited 

 in the erosion troughs and basins. 



Local volcanic vents supplied rhyolitic lavas and acidic 

 tuffs which are frequently associated with the early 

 Tertiary formations. During the Oligocene which con- 

 tinued the erosive work of the Eocene, crusta 



