652 



ALFRED W. G. WILSON 



because the numerous outliers north of the edge of the escarp- 

 ment indicate that the surface over which the average gradients 

 on the Archaean have been taken has been at one time buried 

 beneath the sediments, and this surface has a remarkably even 

 sky-line. 



- In the province of Manitoba, at Deloraine, a well has been 

 driven to a depth of 1,943 feet below the surface and 108 

 feet into the Dakota sandstone. The bottom of the well lies 

 about 299 feet below sea-level and 1,009 ^^^t below the surface 

 of Lake Winnipeg. The Archaean surface beneath the sediments, 

 making no allowance whatever for Silurian and Ordovician 

 sediments which probably underlie this sandstone, must thus 



Fig. 14. 



have a gradient of about six feet per mile, and probably it is 

 actually more than double this amount. East of Lake Winnipeg 

 the gradient upon the Archaean to the summit of the sub- 

 divide, along the same line, is less than two feet per mile. 



The relative positions of these two plains (reference to a 

 possible third plain upon the surface of the Paleozoic sediments 

 is here omitted) suggest certain problems, which may be sum- 

 marized thus : 



1. Do these two plains represent two distinct periods of 

 planation ? 



2. Are AB and BC of the same age, but now discordant by 

 warping ? 



3. Did the former plain AB once extend upward in the 

 direction of BF? 



4. Is the discordance between AB and BC produced by 

 warping ? 



It should be added that the data at present in hand are not 



