PART II 



PRE-DEVONIAN PALEOZOIC FORMATIONS 



The pre-Devonian Cordilleran seas, as far as known, were 

 persistent for long periods, during which large accumulation? of 

 sediment were deposited in the troughs that were formed from time 

 to time in the Cordilleran Geosyncline. Sometimes -deposition was 

 going on in two or more of these minor troughs at the same time, 

 and at other times possibly only in one, as in the case of the Goodsir 

 Trough in Upper Cambrian time. In the closing period of Lower 

 Cambrian time, the sands and arenaceous and siliceous silts were 

 embedding the Mesonacidae fauna in the Beaverfoot Trough on the 

 west and along the eastern shore of the Bow Trough on the east, and 

 again later the Lyell, Sabine, and Mons limestones were being de- 

 posited in the Beaverfoot and Sawback Troughs, the intervening 

 stretches of the geosyncline being separated by barriers or else 

 elevated above the water and not receiving deposits. To the north, 

 however, the Beaverfoot and Sawback Troughs extended as open 

 seaways into the Glacier Lake Trough, permitting the Cambrian 

 and Ozarkian faunas to pass freely between them for a long period. 



Fluctuations in the depth and extent of the seaways in the troughs 

 resulted in more or less abrupt changes in the extent, character, and 

 thickness of the deposits, and in the consequent succession of faunas, 

 the latter receiving at varying intervals new accessions from the 

 Pacific Ocean on the south and west and from the Arctic Ocean on 

 the north. 



In some areas, changes in extent and depth resulted in accumula- 

 tions of sediments, and in others diastrophic movements caused a 

 tilting of the bottom of the seaways, so that very little deposition, 

 if any, took place for considerable periods, while in not far distant 

 areas or troughs one or more geological formations or parts of forma- 

 tions were deposited. The shallowing of the seaways towards the 

 eastern and western shores and at times within the minor troughs 

 resulted in irregular and overlapping deposition, and often in non- 

 deposition of sediments, that gave rise to unconformities of varying 

 degrees of magnitude, without evident disconformity at the contacts 

 between the newer and older formations. This occurred in Cambrian, 

 Ozarkian, and later Paleozoic time. One of the most marked uncon- 



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