Our North-West Prairies. 147 



the annual decay of the ordinary prairie grasses, and per- 

 haps of forest trees. The elevation which took place in the 

 land was greatest at the Eocky Mountains and the different 

 steppes between these mountains and the eastern limits of 

 the prairie, would seem to indicate different stages or inter- 

 vals in the elevation during which the various sandhills and 

 stretches of sand at the extended edges of these steppes have 

 been formed. The contraction in the area of this inland 

 ocean took place from the Eocky Mountains eastward, so 

 that the present Province of Manitoba east of the Duck, 

 Eiding and Pembina Mountains, is the most recently formed 

 as well as the lowest in level. Between the mouth of the 

 Saskatchewan at Grand Eapids and the Assiniboine Eiver 

 between Portage la Prairie and Winnipeg and thence to the 

 United States boundary line, there is not much difference 

 in level, as the following heights above the sea indicate : 



Lake Winnipeg 7 10 feet. 



St. Martin's Lake 737 " 



Lake Manitoba 752 " 



Eiver Assiniboine, near Baie St. Paul.. .. ... . 766 " 



Lake Winnipegosis 770 " 



Cedar Lake, near Grand Eapids, on the 



Saskatchewan 770 " 



This comparatively level area occupies a stretch of 

 country 330 miles in length by an average of 150 miles in 

 breadth. 



Lakes Winnipegosis and Manitoba, and St. Martin's and 

 Water Hen Lakes, are mere shallow depressions on the sur- 

 face of the prairie. The two first named lakes are each 

 over a hundred miles in length, but increase in depth so 

 gradually that at the narrows where they nearly unite, 

 Winnipegosis has only six feet of water at 2,000 feet from 

 the shore, whilst Lake Manitoba, at a mile from the shore, 

 shows a depth of only three feet. St. Martin's Lake, again, 

 has only eight feet, and Water Hen Lake an average of three 

 feet of water. Lake Winnipeg is deeper, being an average 

 of forty feet to sixty feet, with a somewhat uniformly level 

 bottom, but it is relatively very shallow for a lake of its great 



