Handbook of Paleontology 221 



eastern Canada to Alabama, but are confined to the east- 

 ern part of the geosyncline. Middle Cambrian deposits 

 with Par ad oxides occur in northern Vermont and in 

 Newfoundland and eastern Massachusetts. Some of the 

 Arctic and Cordilleran Middle Cambrian faunas passed 

 south from east Canada to Alabama in more western 

 troughs, now doubtless buried under overthrusted de- 

 posits in most of the St Lawrence valley and all of eastern 

 New York but exposed from Pennsylvania southward. 

 The Upper Cambrian is absent north of central Pennsyl- 

 vania but northern types occur in southern Pennsylvania 

 and southern types are found in great development from 

 southern Virginia to Alabama. Late L T pper Cambrian 

 occurs only in and to the west of the Mississippi valley. 

 The great difference in thickness of the formations of 

 Cambrian deposits in different regions, which varies for 

 the period from a few hundred to 12,000 feet, is mainly 

 due to the oscillating seas and the relative availability of 

 the clastic materials. 



The greatest deposits of Cambrian rocks in North 

 America were laid down in the Cordilleran trough, and 

 their remnants which are found today in southeastern 

 California, Nevada, the mountains of Utah and the 

 Canadian Rockies constitute the most extensive and most 

 complete series in the world, yet known. They were 

 made the subject of prolonged study by the late Dr 

 Charles D. Walcott, leading student of Cambrian faunas 

 and their sequence. In the Appalachian trough the rocks 

 of this system show a greater thickness to the north 

 and south of the eastern New York area. In the north 

 the most noted localities occur in western Newfoundland 

 and on the shores of Labrador, the deposits of which are 

 in accord with and may at one time have been continuous 



