TKACTS OF GRAVEL AND SAND. 181 



BELT OF MODIFIED DRIFT BETWEEN ST. PAUL AND VIXNlPEd. 



Modified drift, consistiug of stratified gravel and sand, with local de- 

 posits of clay, overlies the bed-rocks and the till, and generally forms the 

 surface, on an extensive area about the southwest jjart of the Lake of the 

 Woods and along the Rainy River. Southward similar deposits cover large 

 tracts in Mimiesota, reaching to the lakes at the sources of the Mississippi 

 and to the Leaf Hills, and thence southeastward to Minneapolis and St. 

 Paul. The contour of the greater part of these deposits is flat or moder- 

 ately undulating, and their surface varies in height from a few feet to 50 

 feet or rarely more above the adjoining lakes and streams. Li central 

 Minnesota these tracts of gravel and sand have an elevation that increases 

 from south to north, being 825 to 950 feet above sea-level in the ^^cinity of 

 Minneapolis and St. Paul, rising gradually to 1,200 feet iu the distance of 

 .about 100 miles northwest to Brainerd, and ranging from 1,350 to 1,500 

 feet between the Leaf Hills and Itasca Lake. Thence their surface sinks 

 to 1,150 and 1,075 feet in the vicinity of Rainy River and the Lake of tlie 

 Woods. West of this lake, gravel and sand cover most of the country for 

 nearly 75 miles to the upper part of the Roseau, Rat, and Seine rivers, 

 declining in this distance to about 900 feet above the sea. Northwestward 

 these deposits continue to a remarkable group of eskers and small plateaus 

 of gravel and sand, between 750 and 875 feet above the sea, 7 to 15 miles 

 east-northeast of Winnipeg, of which Birds Hill, beside the Canadian 

 Pacific Railway, is the most western and one of the most conspicuous. 



This broad belt of country, characterized by extensive gravel and sand 

 deposits overlying the till, reaches from south-southeast to north-northwest 

 about 400 miles. From Red Lake, in Minnesota, north to the Rainy River, 

 the Lake of the Woods, and the vicinity of Winnipeg, it lies within the 

 area of Lake Agassiz. On each side this lielt is bordered by areas of 

 nearly the same general elevation, which have mostly a surface of till; and 

 it is to be remarked that the heights of the tracts of niodified drift and till 

 are alike determined by that of the underlying rocks on which tliese super- 

 ficial deposits are spread as a sheet of slight depth in com})arison witli the 

 gradual change in then- elevation. The ch'ift sheet on thi.s l)elt, including 

 both the sand and gravel and the underlying deposits of till, probably 



