220 THE GLACIAL LAKE AGASSIZ. 



At the time represented by the Stonewall beach, lying- next in descend- 

 ing order, the surface of Lake Agassiz was 10 to 20 or 25 feet above Lake 

 Manitoba, 5 to 15 or 20 feet above Lake Winnipegosis, and about 110 and 

 140 feet, respectively, above the southern and northern ends of Lake Win- 

 nipeg. It yet extended nearly 40 miles south of the international bound- 

 ary, to the vicinity of the mouth of Park River. 



In receding from the Stonewall to the Niver\-ille stage Lake Agassiz 

 sank below Lakes Winnipegosis and Manitoba, which remain as two of the 

 three large remnants of this vast body of water. On the line of the tram- 

 way at the Grand Rapids of the Saskatchewan Mr. Tyrrell reports four 

 beach ridges of gravel and sand, as already noted, at the heights of 850, 

 805, 800, and 790 feet above the sea. The first is referable to the Stone- 

 wall stage, and the three others to the Niverville stage, which is here 

 compound, apparently on account of intermittent northward uplifting of 

 the country. Mr. Tvrrell informs me that the Niverville beach on Black 

 Island, in the southern part of Lake Winnipeg, is about 60 feet above the 

 lake. At the Grand Rapids, 175 miles northwest from Black Island, its 

 three ridges, in descending order, are 95, 90, and 80 feet above the lake, 

 showing that there was a northward uplift of 15 feet along this distance 

 during the Niverville stage, and that since then a further differential tilting 

 of about 20 feet has taken place. The southern end of the Niverville 

 level of Lake Agassiz was near Morris, Manitoba. It failed to reach into 

 the United States by a distance of about 25 miles, being the first stage of 

 this glacial lake that lay wholly in British America, and it was the latest 

 stage held by the ice barrier and recorded by a well-marked shore-line. 

 Lake Agassiz at this time, as during several preceding stages, reached far 

 north and northeast of Lake Winnipeg, and up to its latest year it may 

 have had an area of 20,000 or 30,000 square miles. 



Finally the retreat of the ice-sheet uncovered the land across which 

 the Nelson outflows from Lake Winnipeg to Hudson Bay. The existence 

 of the glacial lake was ended, and this largest of the great lakes of Mani- 

 toba was added to the number of its present representatives or descend- 

 ants. Dr. Bell's descriptions of the outlet of Lake Winnipeg and the 



