262 ENVIRONMENT OF VERTEBRATE LIFE, ETC. 



Province. There is little doubt that the deposits along the Pacific coast 

 were made in a sea which was in more or less open connection with the one 

 which lay over British Columbia, but all of the sedimentary deposits of the 

 eastern sea have been so disturbed by earth movements and so seriously 

 metamorphosed that the correlation can only be made in a very broad way. 

 One thing is becoming increasingly evident that the limestones and asso- 

 ciated clastic sediments of Alaska and western Canada were deposited in a 

 sea of late Pennsylvanian time, equivalent to the Gschelian. 



In late Pennsylvanian an uplift, first apparent in northern Alaska, devel- 

 oped and spread to the south. This movement was accompanied by much 

 diastrophism and vulcanism which, with later phenomena of like kind, have 

 sadly obscured the record. The effect of the whole movement was to raise 

 the surface above the plane of marine deposition during Permo-Carboniferous 

 time and no traces of terrestrial deposition or erosion during that time have 

 as yet been detected. 



This uplift was of the first importance and had a two-fold effect upon the 

 geography and the environment of life during Permo-Carboniferous time: 

 (i) The movement of the uplift was progressive from north to south, at 

 right angles to the progressive movement of uplift of the continent through- 

 out late Paleozoic. It is very probable that the progressive uplift from 

 north to south, exerting most of its effect farther west, penned in a part of 

 the sea which occupied the northern half of the Basin Province in Pennsyl- 

 vanian time and converted it into the relict seas of Permo-Carboniferous 

 time in which were deposited the phosphate shales and limestones of the 

 Park City formation. (2) The uplift converted the northwestern part of 

 the United States and the western part of Canada into an upland which 

 joined the northern end of the Rocky Mountain barrier between the two 

 provinces and prevented the accumulation of Permo-Carboniferous sedi- 

 ments north of the international boundary. The land area thus formed 

 furnished a reasonable route of migration for the Gigantopteris flora from 

 its home in Asia to the location in Texas where it has been found. 



The upper limit of Permo-Carboniferous time or "Permo-Carboniferous 

 conditions" is as yet undeterminable with any exactness. In the regions 

 where Triassic red beds overlie those of Permo-Carboniferous age, there is 

 no evidence of earth-movements of any magnitude, but there is constant 

 evidence of an increasing aridity which became so vigorous as to be a 

 prominent, if not the dominant, factor in the change of vertebrate life, so 

 pronounced at the juncture of the two periods. 



