Handbook of Paleontology 227 



separate entrances and probably at different times 

 from the south, the east and the northwest, and spread 

 into the Appalachian trough extending northward into 

 New York and Vermont and thence through the St 

 Lawrence area of Canada. The Cordilleran trough 

 was also invaded, but, since the Lower Ozarkian 

 faunas of the Mississippi valley and New York are 

 almost totally different, the former was evidently in- 

 vaded from the Arctic side of the continent. The Cor- 

 dilleran formations are all of Lower Ozarkian time. In 

 late Ozarkian time the seas were greatest in the south- 

 ern part of the Appalachian trough and the Mississippi 

 valley. The Ozarkian deposits are chiefly dolomites 

 and relatively pure limestones and these deposits in the 

 southern Appalachian valley alone aggregate about 

 8000 feet, giving a volume of limy deposits that on the 

 basis of thickness alone would rank the Ozarkian 

 among the most important of the Paleozoic systems. 

 At the very close of the Ozarkian period the continen- 

 tal seas appear to have withdrawn widely from the 

 interior of North America. There was a period of land 

 elevation which, because it involved the Green Moun- 

 tains area of Vermont, has been termed the Green 

 Mountain Disturbance. Through the formation of 

 these highlands a period of erosion was inaugurated. 

 They supplied the materials which go to make up 

 the basal conglomerates of the following period, the 

 Canadian, which is set off from the Ozarkian by an 

 unconformity. 



Life. In the discussion of the life of these periods it 

 must be remembered that there are two faunal prov- 

 inces to be considered, a Pacific Province and an Atlantic 

 Province. The Pacific Province was the larger in North 



