RELATIONSHIP OF BIRDS HILL TO LAKE AGASSIZ 423 



of the central part of the ice-sheet. Finally the area crossed by the Nel- 

 son Eiver and the basin of Hudson Bay were uncovered, allowing the 

 glacial lake to be wholly drained away, excepting its present representa- 

 tives, Lakes Winnipeg, Manitoba, and Winnipegosis, lying in hollows of 

 the land. 



Meanwhile, through the greater part of the time of existence of Lake 

 Agassiz, this part of the earth crust, unburdened by the melting of the 

 thick and heavy ice-sheet, was gradually rising, and its greatest uplifting 

 took place in the central part of the formerly ice-covered area. Thus 

 the successive early shorelines of Lake Agassiz were much uplifted, with 

 all the lake basin, most in the central region of the continental glaciation, 

 and least about its boundaries. This continental uplift gave to the 

 highest and oldest shore a northward ascent that averages nearly a foot 

 per mile for 400 miles from the southern mouth of the glacial lake. Its 

 lower and later shores are each less inclined than the preceding, until the 

 lowest beach is scarcely changed from its original horizontality, showing 

 that the great uplift of this lacustrine area was practically completed 

 before the ice-barrier on the lower part of the course of the Nelson Eiver 

 disappeared. 



A part of a very sandy beach ridge of Lake Agassiz adjoining the east 

 end of this esker has been much excavated for the use of its sand by the 

 Birds Hill Sand Company, as before noted. 



iVgain, about a mile and a half west from that place a more typical 

 but smaller beach ridge is crossed by the roads on the north and east 

 lines of section 28, township 11 north, range 4 east, about 2 miles south- 

 east of Birds Hill Station. This beach, running from northwest to 

 southeast, crossed by each road about 20 rods from the northeast corner 

 of this section, is excavated to depths of 3 to 5 feet at the roadside, and 

 is seen to be fine gravel and sand. Much of the beach deposit consists 

 almost wholly of pebbles from 1 to 3 inches in diameter. It is a very 

 low, gently rounded ridge, about 4 to 6 rods wide, elevated at its crest 

 only 3 or 4 feet above the land adjoining its northern side, which is close 

 to the depressed and till-covered part of the esker's course. The south- 

 western and lakeward side of the beach ridge has a descent of some 5 or 

 6 feet in 3 or 4 rods, to the edge of the very slowly declining flat lowland 

 of till next south, where the lake at the time of its accumulation of the 

 beach had a depth of 2 to 5 feet. 



Both of these beach deposits, observed only for short distances, prob- 

 ably belong to the lowest or Niverville stages of Lake Agassiz, represented 

 near Niverville, Otterburne, and Morris, south of Winnipeg, by small 

 beach ridges, 2 to 4 feet high, whose crests vary from 777 to 784 feet 



