146 Canadian Record of Science. 



margins, each year forming a deposit there on the lake bot- 

 tom and gradually thus increasing the encroachments of the 

 land upon the water. 



There is strong evidence which seems to point to the fact 

 that about the close of the drift period, or immediately after 

 it, when the glaciers, probably, were slowly retreating, the 

 central portions of the continent formed the bed of a vast 

 fresh water inland sea, of which Lakes "Winnipeg, Manitoba 

 and Winnipegosis, are now the mere remnants. The outlet 

 of this sea to the ocean was probably at that time by way of 

 the Mississrpi Valley. Into this sea the glaciers from the 

 Eocky Mountains and from the country north and east of 

 the Saskatchewan, perhaps for long periods of time, flowed, 

 and huge icebergs freighted with boulders, debris and earth 

 were continuously floated off to wend their way at the will of 

 winds and currents. It was not the first time during the drift 

 period that this part of the country had been under water. 

 The resemblance to the Polar Seas of to-day was probably 

 very striking, except in these points that the icebergs 

 would be more deeply sunken, for the water was fresh, and 

 that this inland sea was more vast, covering not merely our 

 North- West prairies, but extending probably as far south 

 as Iowa and Illinois. Boulders were thus scattered at ran- 

 dom over the bottom of the sea hundreds of miles away from 

 their point of origin. Huge masses were carried enormous 

 distances. Dr. George Dawson mentions one of the Huro- 

 nian quartizite, lying near the Waterton Eiver, which mea- 

 sured forty-two feet long, forty feet broad and twenty feet 

 high, and which must have come from east of Lake Winni- 

 peg or the Eed Eiver. 



The very uniform nature of the deposits over very great 

 areas would indicate quiet waters, at least in later periods of 

 the occurrence of this inland sea, probably ending, as the 

 land rose, in the creation of vast marshes, like the existing 

 great grass swamps at Westbourne, and on the Boyne Eiver 

 in Manitoba, but on an immense scale. The successive an- 

 nual growth and decay of sedges and grasses in these marshes 

 gave rise to deposits of vegetable loam which have gone on 

 increasing since the rise of the land to its present level, by 



