422 W. UPHAM ESKER NEAR WINNIPEG, MANITOBA 



It is thus evident that when the ice-sheet had so far receded that its 

 border was being melted away in the vicinity of Birds Hill, permitting 

 the esker to be formed by a stream flowing from it, the level of the ice- 

 dammed lake there, about midway between Red Lake and Riding Moun- 

 tain, was about 1,260 feet above the sealevel. Comparing that height 

 with the surface at Winnipeg, 757 feet, at Birds Hill Station, 759 feet, 

 and the level of Lake Winnipeg, 710 feet, we see that the ancient Lake 

 Agassiz was 500 feet deep above the site of Birds Hill at the time of 

 formation of this esker, the lake then being at its earliest and highest 

 stage. 



Further, it seems to me quite surely demonstrated by the described 

 characters of the stratified drift forming this esker of Birds Hill, that 

 its deposition took place from a freely running stream in a channel that 

 was inclosed on the sides by walls of the waning ice-sheet and was open 

 above to the sky. It was not deposited in the still water of a deep lake, 

 between channel walls of ice rising from the land surface; for then the 

 esker gravel and sand and the frontal lower plain adjoining the east end 

 of the esker could not have been spread out as they now are found. 

 Fluvial currents, such as could only exist above the surface of the adjoin- 

 ing Lake Agassiz, brought and laid down the modified drift of the ridge 

 and its terminal plain. Afterward, by the completion of the melting 

 and retreat of the ice-border here, on each side and beneath the esker 

 and plain deposits, they were allowed to sink gradually about 500 feet, 

 until they rested on the land. 



A short summary of the history of Lake Agassiz needs to be added. 

 Beginning as a small lake at the southern end of the wide Red River 

 valley outflowing to the south in a channel where Lakes Traverse and 

 Big Stone now are, it grew in length northward with the recession of the 

 ice-sheet which was its barrier. Beyond the limits of my explorations 

 of its shorelines, passing through Minnesota, North Dakota, and southern 

 Manitoba, north to the Riding Mountain, its farther extent northward, 

 by Riding and Duck mountains and the Porcupine and Pasquia Hills 

 and across the Saskatchewan River, has been explored by J. B. Tyrrell 

 for the Canadian Geological Survey. Its length grew to at least 700 

 miles, and its area doubtless exceeded 100,000 square miles, surpassing 

 the combined areas of the Great Lakes tributary to the Saint Lawrence. 



After the formation of the uppermost or Herman beach, a series of 

 several lower beaches with outflow still to the south was formed by the 

 downward erosion of the channel of the outflowing river. Still later a 

 la^ge series of yet lower beaches recorded the successive lower outlets of 

 the lake while it outflowed northeasterly, previous to the full meltinff 



