570 DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



8. The Eastern Geosynclinal Belt was little affected by these great crustal 

 and subcrustal movements in the west. Its Paleozoic beds still lay widely flat, 

 with their surface probably but little above the sea through the whole of the 

 lower Mesozoic. The Jurassic revolution of the west had no more affected these 

 strong rocks than the Alleghany plateau region was affected by the force 

 which set the strata of Virginia and Pennsylvania writhing into sharp folds 

 at the close of the Paleozoic. At the very close of the Jurassic there was, 

 apparently, a slight submergence of the eastern edge of the Eastern Cordilleran 

 Belt beneath the mediterranean waters of North America ; perhaps this slight 

 movement was an echo of the strife of force and matter along the Pacific. 



9. Extremely rapid erosion of the new Jurassic mountains in the west 

 uncovered some of the granitic batholiths, thus removing thousands of cubic 

 miles of rock from these mountains. Some of the clastic material was, during 

 the Cretaceous (Shasta-Chico) period deposited in local geosynclines formed 

 on the Jurassic granites or on older formations. Local vulcanism initiated 

 the downwarp in at least the one case of the Pasayten Cretaceous geosyncline. 

 Besides the 1,400 feet of pyroclastics thus formed, some 29,000 feet of sand- 

 stone, conglomerate and shale were deposited in this one downwarp. 



10. While the Pasayten, Queen Charlotte, and other of these local geosyn- 

 clinals - were forming in the Western Belt, the Eastern Belt was similarly 

 affected by downwarps and the formation of sedimentary prisms of geosynclinal 

 thickness. The nearest demonstrated geosynclinal belonging to this period 

 is that in the Crowsnest district, but further study may show that the Creta- 

 ceous beds attained a thickness of over 6,000 feet at the Forty-ninth Parallel 

 itself. 



Meanwhile the eastern half of the Western Cordilleran Belt and the western 

 half of the Eastern Cordilleran Belt formed a broad and fairly continuous area 

 of land; from it the geosynclinals to east and west were fed with detritus. The 

 central land-mass seems-'to have been locally the scene of heavy volcanic action, 

 typified by the younger basic effusives in the Bossland district. The reader will 

 remember, however, that the dating of this particular part of the Rossland 

 volcanic group is very uncertain; perhaps it should be referred to the Jurassic 

 or even the Triassic. 



11. When the larger Cretaceous geosynclinals reached critical depths, the 

 post-Laramie or ' Laramide ' revolution took place. The structural turmoil 

 of the already crumpled Paleozoic and Triassic rocks in the Western Geosyn- 

 clinal Belt was greatly enhanced. A deformation almost as intense was simul- 

 taneously produced in the Eastern Geosynclinal Belt. The gigantic overthrusts 

 and horizontal shifts, so marked in the Selkirk, Purcell, Clarke, and Lewis 

 ranges, were probably then caused, although Willis notes the alternative possi- 

 bility that the Lewis thrust dates from the mid-Tertiary. Much of the normal 

 faulting characteristic of the Purcell and other ranges is most likely to have 

 been produced in the late stage of the Laramide revolution. 



12. So great an orogenic revolution, the only general occurrence of the 

 kind in the whole Cordillera in these latitudes since the pre-Cambrian, might be 



