630 W, A. JOHNSTON 



by a relatively high area which rises to a maximum height of about 

 200 feet above the general level of the plains. The area lying 

 between Rainy Lake and Lake of the Woods is so deeply drift- 

 covered that comparatively few solid-rock exposures occur. The 

 surface has generally very slight relief, and slopes gently toward 

 the west, so that the area really forms a portion of the eastward 

 extension of the wooded portion of the prairie plains of Manitoba 

 and northern Minnesota, from which it is separated by the shallow 

 basin of the southern portion of Lake of the Woods. In the north- 

 ern portion of Lake of the Woods and north of a line drawn from the 

 central part of the lake southeastward to Rainy Lake, the country is 

 generally rocky and has comparatively little drift covering. 



Till sheets. — There are at least two distinct till sheets in the 

 district. The upper and younger is distinguished from the lower 

 and older till sheet by the calcareous nature of its materials, and 

 by the presence in it of bowlders of limestone and other rocks which 

 are known to outcrop in Manitoba, but not in the district itself 

 nor in the region lying to the northeast. Striae observed on the 

 bedrock beneath the till sheet trend southeastward or eastward. 

 These striae were not seen to be crossed by later striae, and no till 

 was seen to overlie this till sheet. It scents evident, therefore, that 

 the calcareous till was deposited by a lobe of the Keewatin glacier 

 and that the area in which the calcareous till occurs was not over- 

 ridden by an advance of ice from the northeast at a later time. 



The lower and older till sheet was deposited by an ice sheet 

 advancing from the northeast. This is shown by the southwest- 

 ward trend of striae on the bedrock underlying this till sheet and 

 by the fact that the till contains no limestone similar to that which 

 occurs in the upper sheet. Associated with the lower till sheet are 

 considerable deposits of fluvio-glaeial sands and gravels which also 

 contain no limestone. Xo evidence was seen which would suggest 

 that there was any considerable lapse of time between the depo- 

 sition of the two till sheets, and it is presumed that they were nearly 

 contemporaneous in age and were deposited during the Wisconsin 

 stage of glaciation. 



Laminated stony clays. — A series of laminated clays, containing 

 in places striated stones and bowlders, occurs in the district. The 



