16 Mr. W. Topley on the Physical 



crystals in their normal condition present equal elasticity in all 

 directions ; hence, when placed between crossed Nicols, they 

 exhibit no depolarising action, and the field consequently 

 remains dark throughout a complete revolution of the stage. 



46. — Notes on the Physical Geography and Geology of 



Western Canada. 



By W. Topley, P.G.S., Geological Survey of England, President 

 of the Geologists' Association. 



(Bead November 12th, 1884.) 



The object of this address was to give a brief account of the 

 Physical Geography and Geology of Western Canada, and more 

 especially of such parts of the country as were seen during the 

 excursion of the British Association to the Eocky Mountains. 

 Starting from Toronto, the party took rail to Owen's Sound ; 

 then steamer over Lakes Huron and Siiperior to Port Arthur ; 

 then again the railway past Winnipeg, and over the prairies to 

 the Rocky Mountains. 



The country between Lake Superior and the Eockies may 

 be divided into four zones, each coiTCsponding with geological 

 structure. 



{a). The most easterly zone is that between Lake Superior 

 and the Eed Eiver Valley. This is a wooded hilly region, formed 

 chiefly of crystalline Laurentian rocks, the oldest rocks known. 

 The rocks lie at steep angles, often almost vertical, the edges of 

 the beds having been worn away by long continued denudation. 

 In long past geological times these Laurentian rocks may have 

 stood up as great mountain chains ; but wliat we now see are 

 only the stumps and cones of the old mountains. The latest 

 denudation has been that of the glacial period, when a great 

 sheet of ice overspread the whole of Canada, and stretched far 

 into the United States. The evidence of this is seen in the 

 grooved and polished surface of the rocks, when these are 

 freshly exposed, and in the deposits of boulder clay and gravel 

 which overspread the country. 



These deposits, over the district traversed by the Canadian 

 Pacific Railway, are not sufficient to entirely cover up the solid 

 rocks ; the general character of the country is rocky with 

 marshy hollows, which are in some cases due to ice-worn 

 hollows in the solid rock, and sometimes to deposits of drift 

 blocking the drainage. In these marshy hollows the vegetation 

 is peculiar, as is described by Mr. Meuuell in the next paper. 

 The whole of this area is unsuited for settlement, the soil being 



