THE LAURENTIAN PENEPLAIN 617 



It is not proposed in the present paper to enter upon any discus- 

 sion of the strictly geologic problems offered by the rocks of 

 the area — such as a consideration of the stratigraphy, origin, 

 and relations of the metamorphic and igneous rocks of the great 

 Archaean complex. 



THE CANADIAN OLDLAND. 



In its general features eastern North America presents in a 

 most striking manner and on a large scale what may be regarded 

 as a typical development of physiographic forms characteristic 

 of a belted ancient coastal plain centered around an oldland 

 area. The Canadian shield of Suess, the area whose general 

 physiographic features are to be more particularly described and 

 discussed in the succeeding pages of this paper, marks the site 

 of the oldland area from which the materials of the later sedi- 

 mentary deposits were derived. A reference to the accompany- 

 ing sketch map (inset) will show the general U form of this 

 oldland area, which extends from Coronation Gulf in the extreme 

 northwest, southward around Hudson Bay and northward through 

 Labrador to Baffin Land and beyond. Its width varies from 

 nearly a thousand miles in Labrador to about two hundred miles 

 in the country southwest of James Bay. 



Bordering the oldland on its convex side, and extending 

 from the island of Anticosti in the Gulf of the St. Lawrence 

 westward and northward as far as the Arctic circle, and probably 

 beyond, we have a series of land forms presenting on the grand- 

 est scale the general features of an ancient belted coastal plain, 

 in its present aspect much modified, it is true, from normal form 

 — a modification probably due to the operation of relatively 

 recent processes, differential uplift, and glacial action. The 

 belted coastal-plain features are best preserved in the region of 

 the Great Lakes. The most prominent topographic feature of 

 this costal plain is the Niagara cuesta, which can be traced with 

 varying expression from near Rochester, on the south shore of 

 Lake Ontario, westward as far as the state of Wisconsin, beyond 

 which it disappears for a time beneath the drift, but reappears 

 to the west of Lake Winnipeg. Lakes Erie, Huron, Michigan, 

 Manitoba, and Winnipegosis are situated u[)on the outer lowland ; 



