884 GEOLOGY 



of the ice in the Mackenzie and Hudson Kay basins, but little is yd 

 known regarding them. 



A very important lake was formed in the Red River valley of 

 the North (Lake Agassiz, Fig. 590), discharging, in its earlier history, 

 into the Minnesota River at Lake Traverse. Lake Agassiz was not 

 connected with the complex system of basins of the St. Lawrence 

 valley, and had a comparatively simple history. It grew to the 

 northward with the retreat of the ice which held it in at that end, 

 and continued to discharge into the Minnesota River until the retreat 

 of the ice gave it a northerly outlet. It developed beaches while it 

 discharged to the southward, and another set after the outlet wus 

 northward. On the final withdrawal of the ice, the lake was drained. 



The evidence which demonstrates the existence of these ex- 

 panded lakes is found chiefly in the deposits which they made, and 

 in the topographic features which they developed about their shores. 

 Many of the former shore-lines have been traced in detail, and most 

 of them depart notably from horizontality. In general, they rise 

 to the north and northeast. 



It is probable that there were corresponding lacustrine sub- 

 stages at the close of each of the several glacial epochs, but their 

 history is not known. 



XL The Champlain substage. 1 The significant feature of this 

 stage is represented in Fig. 589, which represents an arm of the 

 sea extending up the St. Lawrence to Lake Ontario, filling the basin 

 of Lake Champlain, and probably connecting southward by a 

 narrow strait along the site of the Hudson valley with the ocean. 

 The sediments deposited in this arm of the sea contain shells and 

 bones of marine animals. The marine fossils are found at various 

 places about Lake Champlain at altitudes varying from 400 feet <>r 

 less about the south end of the lake, to 500 feet at the north end. 

 and about 600 feet near the east end of Lake Ontario. 2 



*Peet, Jour. Geol., Vol. XIII (1904), pp. 415-469, 617-061; Salisbury. 

 Glacial Geol. of N. J., pp. 196-200; also Ries and Merrill, 10th Ann. Rrp' 

 N. Y. State Geologist, 1890; Ries, Bull. N. Y. State Mus., Vol. III. 1 

 Baldwin, Ann. Geol., Vol. XIII, 1894; Davis, Proc. Bos. Soc. Nat. Hist.. Vol. 

 XXV, 1891; Upham, Bull. Geol. Soc. Am., Vol. Ill, 1891; Kellogg. Sri. 

 Vol. XIX, 1892; and Woodworth, Bull. 84, N. Y. State Mus. 



2 Dawson, G. M., Am. Jour. Sci., 3d ser., Vol. VIII (1874), p. 143: I > 

 J. W., The Canadian Ice Age, p. 201, and Am. Jour. Sci., Vol. CX\\ 



