MacMillan : shores at lake of the woods. 953 



and there, however, as at Crow Rock island, such cliffs are 

 conspicuous features. Other cliffs of this kind may be seen in 

 Whitefish bay and in Shoal lake. The ordinary shore line is 

 low and rounded. The islands 1 have previously classified - 

 as 1, Bog islands; 2, Sand dunes; 3, Drift covered islands; 4, 

 Dome-shaped rock islands; 5, Irregular or jagged rock islands. 

 The fourth and fifth classes are by far the most abundant. 



An intelligent notion of the region is conveyed by Lawson 

 when he terms it a flooded area of roches moutonc's. Evidences 

 of profound glaciation are abundant, and the innumerable small 

 islands, which are so characteristic a feature of the scenery, 

 remind one of typical roches moutoneJs. 



The lake is nowhere extraordinarily deep, soundings of 85 

 feet in the northern portion and 40 feet in the Traverse being 

 exceptional. Where the lake is shallower — that is in the 

 southern part — there is a greater amount of drift upon the bot- 

 tom. Thus soundings off Garden island in the Grand Traverse 

 always showed a bottom of blueish clay, while to the north 

 the plummet frequently indicated rock, or organic silt, derived 

 from the planktonic flora and fauna. 



Origin of the lake. — The bed of Lake of the Woods has un- 

 dergone extensive preglacial erosion, but the glacial and post- 

 glacial history of the region is of particular interest in this 

 connection. Lake of the Woods, together with Rainy lake, Red 

 lake, Lake Winnipeg, Lake Manitoba and Lake Winnepegosis 

 lie quite within the bed of a temporary glacial lake known to 

 students of geology as Lake Agassiz 3 . This lake, for about 

 1000 years, covered the Red river valley and portions of the 

 valleys of the Saskatchewan and Assiniboine rivers of Canada. 

 It covered, too, the drainage-basin of Lake Winnipeg, and com 

 prised in all about 110,000 square miles. Rainy lake, tributary 

 to Lake of the Woods, lies just within the southeastern bound- 

 aries of the ancient lake. At first Lake Agazziz emptied into 

 the Mississippi by way of the Minnesota river, but later, for a 

 somewhat shorter time, its waters were drained towards the 

 north. Apparently, as first pointed out by Winchell, the gen- 

 eral northern boundary of Lake Agassiz was the retreating 

 continental ice sheet, and this quite certainly extended near 

 the eastern end of Rainy lake. South of Lake of the Woods 



2 MacMillan. On the distribution of plants in a fresh-water insular region. Ab- 

 stract. Bot. Gaz. 22: 218. 1896. 



3 Upham.W. Lake Agazziz. Mon. U. S. Geol. Surv. 25. 1897. 



