462 THE GEOLOGIST. 
not occur at a great altitude above the present sea-line, and in this deposit Mr. .' 
Baurmau has also found marine shells. 
Next iu 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 f 
Basin, showing that there also the lakes have decreased in size as their waters i 
created channels of escape through the eastern belt of rocky country. These i 
deposits form the level prairies round the Red River settlement, and constitute | 
the first or lowest prairie steppe. I 
The belt of rocky country which divides Hudson's Bay from the St. Lawrence j 
Basin, but is traversed by the rivers that flow from the Winipeg Basin, has an I 
altitude in some parts of 1400 to 1600 feet, and its highest portions are covered i 
by deposits of coarse sand with erratics. This drift deposit does not appear in f 
situations only when sheltered by rocky high grounds, but forms a swampy or I 
wooded plain, the eastern margin of which has been water-worn into deep \ 
gulleys and poi- holes, or circular depressions which have no outlet. The rock j 
surfaces in this region are found to be furrowed by scratches which have a 
southerly trend. 
Passing to the west across the lov/ plains formed of the lake deposits which i 
were before mentioned, we find that they are bounded to the west by an i 
escarpment which marks the eastern limit of the second prairie steppe, which i 
slopes from 1000 to 1600 feet above the sea-level, and is covered often to the I 
depth of several hundred feet with drift similar iu 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 13000 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 disjilay 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, 
the 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- 
reous clay filling all the valleys on both sides of the Rocky 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. 
