218 ENVIRONMENT OF VERTEBRATE LIFE, ETC. 



have been derived from the newly emerged Eastern belt. The ancient relation 

 of the two belts was thus reversed, except for local, temporary embay ments on 

 the east. This movement was, apparently, felt from Alaska to northern Utah at 

 least; farther south, in the region of the fortieth parallel, the reversal of relations 

 was postponed to the close of the Pennsylvanian period. Otherwise the Eastern 

 and Western belts have respectively behaved as units in the momentous change. 

 The larger part of the Eastern belt was to remain as land through the Permian, 

 Triassic, and most of the Jurassic periods; and even in the later periods to undergo 

 only partial submergence. 



"The new relation between the two cordilleran belts was so similar to that 

 which obtained on the line of the fortieth parallel at the close of the Upper 

 Carboniferous period that it is instructive to review King's statement, published 

 on pages 536-537 of the volume on Systematic Geology, Fortieth Parallel Survey: 



"After the close of this great conformable Paleozoic deposition widespread 

 mechanical disturbance occurred, by which the land area west of the Nevada 

 Paleozoic shore became depressed, while all the thickest part of the Paleozoic 

 deposits from the Nevada shore eastward to and including the Wasatch rose 

 above the ocean and became a land area. Between the new continent and the 

 old one which went down to the west, there was a complete change of condition. 

 The land became ocean; the ocean became land. * * * 



' ' Upon the western side of the new land-mass, the Archaean continent, 

 having gone down, made a new ocean-bottom, and upon this immediately began 

 to accumulate all the disintegration-products of the new land-mass which the 

 westward-draining rivers and the ocean waves were able to deliver. Throughout 

 the Triassic and Jurassic periods the western ocean was accumulating its enor- 

 mously thick group of conformable sediments upon the Archaean floor, * * * 

 until, at the close of the Jurassic age, there had accumulated in the western sea 

 20,000 feet * * * of Triassic and Jurassic material.' 



"During the Pennsylvanian period the main Pacific geosyncline was the 

 scene of heavy sedimentation with accompanying powerful vulcanism. The rock 

 exposures at the forty-ninth parallel do not suffice to show clearly the dynamic 

 events leading to the Triassic, but from Dawson's work in Vancouver Island, as 

 well as on the mainland, it appears that there was local deformation of the 

 Pennsylvanian beds in that part of the cordillera, followed by erosion of the 

 upturned strata, before these were buried beneath Triassic deposits. It is likely 

 that the same crustal movement affected the Forty-ninth Parallel section; and, 

 further, that it is to be correlated with the beginning of the Sierra Nevada down- 

 warp described, as above, by King. How long or how extensive was this tem- 

 porary return to land conditions in the Western Belt can not be declared. It is 

 known, however, that the Triassic period saw, at the forty-ninth parallel, a 

 resumption of marine sedimentation on the Pacific side of the belt. Argillites, 

 sandstones, and limestones, together with great piles of basic volcanic material 

 were then laid upon the Pennsylvanian formations in this region." 



It is apparent from the summary descriptions of the Alaska and British 

 Columbia regions and the conclusions given by Daly that at the latest date 

 in the Paleozoic from which we have sediments preserved the Pacific Coast 

 region, even far south of Alaska, was submerged and probably receiving 

 sediments from the Eastern geosynclinal belt now raised above the level 

 of the sea. It is not so apparent that the northern end of the Eastern belt 



