626 ALFRED W. G. WILSON 



even surface of the area, in almost every part from Labrador 

 south around Hudson Bay to the Arctic Ocean, is found to 

 truncate the structure of intensely metamorphosed igneous and 

 sedimentary rocks, irrespective of their hardness or attitude. 

 The metamorphism is such as to imply that they have been at 

 one time buried deeply beneath the surface of an overlying land 

 mass, and have been subjected to the strains and stresses of 

 intense orogenic movements. The removal of overlying mass 

 of rock must have occupied an immense interval of time. How 

 great it is impossible to say. For part of the area at least, this 

 degradation took place before late Paleozoic time, for we find 

 Paleozoic sediments resting upon a modified peneplain surface. 

 It seems probable that for the central portions the interval was 

 much longer.^ 



In brief, a study of the physiographic features of the Lauren- 

 tian Peneplain must undoubtedly lead to the conclusion that the 

 Canadian shield has been, for an exceedingly long interval of 

 time exposed to processes of erosion which were chiefly subaerial ; 

 and a study of the relations of the central peneplain surface to 

 the surface upon which the Paleozoic sediments around the 

 margin rest shows that at least parts of the peneplain were 

 produced before later Paleozoic times. It is only by stratigraphic 

 studies, however, that approximate dates can be assigned for the 

 origin of specific features. 



FEATURES OF THE PLANATION SURFACE. 



I. Character of the sky-line. — The most dominant and striking 

 feature of the whole region, from the northern part of the interior 

 of Labrador following approximately the median line of the 

 region around to the south of James Bay and northwest toward 

 the Arctic Ocean, is the remarkably even character of the sk}^- 

 line. With few exceptions, to be noted elsewhere, almost 

 everywhere in the interior it is found that from any slight eleva- 

 tion, which lifts the observer above the tree line, the bounding 

 horizon is very even and almost circular. The many traverses 



^ It must be noted in this connection that Lawson, writing in 1888, dissents from 

 the view tliat the Archsean rocks were ever elevated into mountains (18, p. 23). 



