Introduction 7 



of an ice-barrier. Records of the levels are found in at least 

 seventeen different beaches. 



This lake was there so recently — 5,000 to 7,000 years ago, 

 it is estimated^ — that the land it once covered is yet unfurrowed 

 by erosion, and the rivers that cross its bed have not had time 

 to scoop out valleys for themselves. 



Stoney Mountain, rising eighty feet above the plain, is a 

 mass of Hudson River (Silurian) limestone that escaped part 

 of the erosion of the glaciers, and stands in its original posi- 

 tion a monument of former levels and formations. 



Bird's Hill, north-east of Winnipeg, an accumulation of 

 gravel and sand, is now believed to be an **osar," that is, 

 either a glacial river-delta or the slack-water dump where two 

 glacial rivers joined. 



The long gravel ridges formed in various parts of the 

 First Prairie Steppe are the ancient beaches of Lake Agassiz 

 at its different levels. The highest of these is to be seen on the 

 Pembina Mountain, between Morden and Thornhill. Each 

 of these beaches has an upward slope to the northward of about 

 one foot to the mile, showing a total elevation of about 300 

 feet at the outlet of Lake Winnipeg, as compared with the 

 level of the ridges of the former Lake Agassiz opposite the 

 southern part of Lake Manitoba. 



The Second Prairie Steppe finds its eastern border at the 

 west shore line of Lake Agassiz. It includes the rest of the 

 province on that side, except Turtle Mountain, and is 

 bounded westerly by the Coteau du Missouri, or Third Prairie 

 Steppe. 



This second prairie level had apparently two great lakes 

 in early glacial times — one Lake Saskatchewan, the other Lake 

 Souris. The level plains of the Souris country were the floor 

 of the latter, and White-water Lake is its last remnant. At 

 this time we believe Lake Saskatchewan was cut off by the 

 land ice and the Pasquia Hills from Lake Agassiz, and the 



» Dr. George Bryce, Surface Geol. Red River. Trans. Hist, and Sci. Soc. Man., 

 No. 41, 1891, p. I. 



