226 New York State Museum 



Cordilleran trough were of wide extent during this 

 epoch, especially in the Mississippi basin, and these 

 waters of mainly Pacific and Arctic origin at times 

 also entered the southern part of the Appalachian 

 trough. The uplands of the Killarney mountains pre- 

 vented these waters from spreading north of the Lake 

 Superior-Lake Huron region. The deposits of this time 

 in the Cordilleran trough and the southern Appalach- 

 ians range in thickness from 3000 to 4000 feet, most of 

 the material being limestones. The Upper Cambrian 

 in the Arbuckle mountains is less than 500 feet thick 

 and largely of sandstone. In the strata of the upper 

 Mississippi valley sandstones predominate and these 

 were derived from the residual material formed by 

 long-continued erosion of the crystalline low land of 

 the Canadian Shield. The Upper Cambrian of the At- 

 lantic Province (Bretonian) has its greatest thickness 

 in Cape Breton and the New Brunswick region. The 

 Upper Cambrian as denned here does not appear in 

 the northern part of the Appalachian trough. 



The Ozarkian system of rocks is separated from the 

 Upper Cambrian (St Croixian) beds by a break or 

 unconformity and is marked by a great difference in 

 the character of the fauna. Deposits of the period 

 have been found outcropping from New York and Ver- 

 mont south through New Jersey and Pennsylvania to 

 Alabama, in the Mississippi basin (Missouri, Iowa, 

 Wisconsin, Minnesota, Oklahoma), central and west- 

 ern Texas, Colorado, Idaho and Nevada. They have 

 also been found in British Columbia and it is believed 

 with good reason that the system is represented in 

 western Quebec and possibly northern Newfoundland. 

 The Lower Ozarkian sea invaded the continent by 



