100 THE GLACIAL LAKE AGASSIZ. 



River Valley plain south and southwest of the Silurian area. Tracts of the 

 Dakota sandstone probably supply the brackish water which is found by 

 many wells in this valley, similar to the water derived from this sandstone 

 by deep artesian wells at Tower City and Devils Lake, along the James 

 River, and on higher land in South Dakota west of the James Valley. 



FORMER EXTENT OF CRETACEOUS BEDS EASTWARD ON THE AREA 

 OF LAKE AOASSIZ, 



East from the foot of the highlands of Pembina, Riding, and Duck 

 mountains and the hills farther north, Cretaceous strata have not been 

 found, so far as I have learned, in Manitoba, nor in the region north and 

 northeast from Lake Winnipeg to Hudson Bay. It seems quite certain, 

 however, that Cretaceous beds continuous from this escarimieut originally 

 extended east a considerable distance, probably so far as to cover the area 

 now occupied by Lake Winnipeg. As Hind and Dawson have pointed out, 

 it was by the erosion of their eastern portion that this steep line of high- 

 lands was formed ; ^ and it may be expected that thin remnants of them 

 will yet be found in central and eastern IManitoba. 



The eastward continuation of the Cretaceous formations in southei-n 

 and central Minnesota, indicated liy numerous outcrops, has been noticed in 

 the preceding pages. Further evidence of their former extent is afforded 

 in the north i)art of this State by Mr. Horace V. Winchell's discovery of 

 Cretaceous shales in place on the Little Fork of Rainy River, ^ and by the 

 frequent occurrence of lignite in the drift upon the country south of the 

 Lake of the Woods and between Rainy Lake and Vermilion Lake. Possi- 

 bly this lignite may be of interglacial age, like l^eds that are found between 

 deposits of till in southeastern Minnesota, in the basin of the Moose River, 

 tributary to James Bay, and in other places ; but Prof N. H. Winchell 

 thinks that more probably its origin is from lignite-bearing Cretaceous 



'H. Y. Hind, Report of the Assiniboiue and Saskatchewan Exploring Expedition, Toronto, 1859, 

 pp. 168,169; Narrative of the Canadian Exploring Expeditious, London, 1860, Vol. II, pp. 48,55, and 

 265. G. M. Dawson, Geology and Resources of the Forty-ninth Parallel, 1875, pp. 2.53, 254. 



'' Geol. and Nat. Hist. Survey of Minnesota, Sixteenth Annual Report, for 1887, pp. 403-9. 431, 434. 



