TEE GENESIS OF LAKE AGASSIZ 629 



great thickness and extent of these deposits and the occurrence of 

 " sheets of turf" in their lower portions seem difficult of explanation 

 on the assumption that they are " recent fluvial deposits." 



All these difficulties disappear, however, if it is considered, as 

 the evidence seems to show, that Lake Agassiz had at first small 

 beginnings in Red River valley and gradually rose until it over- 

 flowed to the south, owing to a blocking of the northward drainage 

 by an advance of the ice, and that the ice advanced only into the 

 northern portion of the basin, so that the whole southern part of 

 the lake was practically free from ice during the entire existence 

 of the lake. 



RECORDS OF LAKE AGASSIZ IN RAINY RIVER-LAKE OE THE WOODS 



DISTRICT 



Geographical relations of the district. — The eastern portion of 

 Rainy River-Lake of the Woods district lies about midway between 

 Lake Superior and the Red River of the province of Manitoba. 

 The Rainy River connects Rainy Lake and Lake of the Woods and 

 for a distance of 82 miles forms the international boundary between 

 the state of Minnesota and the adjoining portion of the province 

 of Ontario. The Rainy River, the main stream of the region, flows 

 westward to Lake of the Woods, which drains northwestward to 

 Lake Winnipeg and thence to Hudson Bay, so that the whole area 

 lies within the Hudson Bay drainage system. The altitude of 

 Rainy Lake is 1,107 ^ ee t and of Lake of the Woods 1,060 feet above 

 the sea, and the general altitude of the plain bordering the Red 

 River on the west is about 200 feet lower. The southern portion 

 of Lake of the Woods is shallow and is generally bordered by drift 

 deposits. The divide southwest of the lake, separating the lake 

 basin from that of the Red River on the west, is low and for some 

 distance is less than 30 feet above Lake of the Woods. On the 

 northwest, near Northwest Angle, the divide is also only a few 

 feet above the level of the lake, so that the plains of Manitoba and 

 northern Minnesota are practically continuous on the southwest 

 and northeast into the southern portion of the Lake of the Woods 

 basin. In southeastern Manitoba, and west of the southern portion 

 of Lake of the Woods, the continuity of the plain's surface is broken 



