462 



THE GEOLOGIST. 



not occur at a great altitude above the present sea-line, and in this deposit Mr. 

 Baurman has also found marine shells. 



Next in point of altitude, although probably altogether more recent than the 

 first group, come the Lake terraces which surround Lake Superior and the upper 

 part of the St. Lawrence Basin, at an altitude of from 500 to 800 feet. At 

 nearly the same altitude fresh-water deposits are found in the Lake Winipeg 

 Basin, showing that there also the lakes have decreased in size as their waters 

 created channels of escape through the eastern belt of rocky country. These 

 deposits form the level prairies round the Red River settlement, and constitute 

 the first or lowest prairie steppe. 



The belt of rocky country which divides Hudson's Bay from the St. Lawrence 

 Basin, but is traversed by the rivers that flow from the Winipeg Basin, has an 

 altitude in some parts of 1400 to 1600 feet, and its highest portions are covered 

 by deposits of coarse sand with erratics. This drift deposit does not appear in 

 situations only when sheltered by rocky high grounds, but forms a swampy or 

 wooded plain, the eastern margin of which has been water-worn into deep 

 gulleys and pot-holes, or circular depressions which have no outlet. The rock 

 surfaces in this region are found to be furrowed by scratches which have a 

 southerly trend. 



Passing to the west across the low plains formed of the lake deposits which 

 were before mentioned, we find that they are bounded to the west by an 

 escarpment which marks the eastern limit of the second prairie steppe, which 

 slopes from 1000 to 1600 feet above the sea-level, and is covered often to the 

 depth of several hundred feet with drift similar in character to that that covers 

 the eastern rocky district. The third prairie steppe, which bounds these heavy 

 drift deposits to the west, ranges from 2000 to 3000 feet above the sea-level, 

 and is composed of cretaceous strata, but still with a sprinkling of erratics on 

 its surface. The escarpment which the third steppe presents is often an abrupt 

 slope, 500 or 600 feet in height. It follows a line N.W. and S.E., which was 

 seen well marked to the north of the Saskatchewan, and thence sweeping in 

 the above direction with large bays and indentations, but keeping on the 

 whole parallel to the rock tract to the east, and thus forming a trough, through 

 which swept the currents that dispersed the erratics by means of icebergs. 



In the centre of this trough there occur hills which are composed of masses 

 of the cretaceous strata that have remained undisturbed, and which display the 

 feature known as " Crag and Tail," having the one aspect, generally the N. or 

 N.E., furrowed and water-worn, and covered with a profusion of boulders, 

 while in the opposite direction they form a gently sloping plain comparatively 

 free from erratics, the " tail" being in this case without loon blocks, owing to 

 the soft nature of the " crag." 



It is not improbable that the rate of elevation of the east and west sides of 

 this trough has been unequal, for along the base of the escarpment that forms 

 its western margin, enormous boulders of magnesian limestone are deposited 

 at an elevation of not less than 648 feet above the sea, which so far as is 

 known could only have been derived from strata which form the eastern floor 

 of the trough at an elevation of not more than 800 feet. 



Excepting the boulder clay mentioned as occurring on the Gulf of Georgia, 

 Hie later deposits on the western slope of the continent are very different from 

 those on the east, as they consist of well-worn shingle, with sand and calca- 

 neus clay filling all the valleys on both sides of the llocky Mountains from an 

 altitude of 5000 feet to the sea-level. These deposits have generally been 

 moulded by lake and river action into terraces which skirt the valleys. 



