lO ROYAL SOCIETY OF CANADA 



The red boulder clay came from the east;, but no statement is made 

 as to the lower till sheet.^ 



Still farther north the writer refers to eastern erratics on the 

 bioken plateau belt flanking the foothills west of Mackenzie river, and 

 thinks they were probably water borne, since boulder clay was found 

 only 40 miles above the mouth of Liard river, while the erratics extended 

 much farther.2 



Glacial Lakes. 



As suggested before by Tyrrell and others one of the striking 

 features of the plains is the great number of erratic boulders scattered 

 over the surface or slightly buried under the widespread lake deposits. 

 From Calgary and Big Eddy eastwards along the two routes followed by 

 my party one finds vast numbers of boulders of granite, gneiss, and 

 va'rious Keewatin rocks'^^ sometimes many together, sometimes very 

 sparsely scattered; and the pame is true along the railway between 

 Calgary and Edmonton, and farther to the northwest, as shown by Mc- 

 Connell. 



With these Archsoan boulders in some places there are smaller 

 stones, often rounded, originating in the Eocky Mountains. 



These erratics might be accounted for as dropped by the melting 

 of the Keewatin glacier; but v;ere more probably left by floating ice in 

 the great lakes which covered 7nuch of the region toward the end of the- 

 ice age. Tyrrell and McConnell have called attention to the existence 

 of lakes of the kind on the western plains,^ and my own observations 

 confirm their suggestion. Thus far the boundaries of these lakes have 

 not been mapped. The broad areas of flat clay land, and the general 

 covering of silt or clay over the gentle rolls of the plain are best 

 accounted for by the work of Inkes, predecessors of Agassiz, hemmed in 

 by the mountains on the southwest and the Keewatin ice sheet on the 

 north and east. As the ice withdrew, lower and lower outlets would be 

 opened, so that the waters may not have stood at any given level very 

 long. 



As noted by various observers, from Dr. Hector on, along all the 

 rriver valleys just east of the Tuountains there are well marked terraces, 

 partly carved from the soft shale and sandstone, partly built up of sand 

 and gravel. 



1 G.S.C., 1890-1 D. pp. 60-62. 



2 Ibid., 1888-9, p. 24 D. t 



3 Geol. Sur. Can.. 18S0, 143 E ; also Bull. G.S.A., Vol. 1, p. 410. 



