LOWER SASKATCHEWAN RIVER VALLEY. 
3 
wan river. The Grand rapids of the Saskatchewan are formed 
by the river crossing this scarp which is a prominent physio- 
graphic feature lying a few miles back from the lake shore, 
where it maintains a northerly trend for 50 miles or more north 
of the Grand rapids. South of the Saskatchewan this scarp 
becomes a less conspicuous feature. The summit of the scarp 
affords the most promising route in the Saskatchewan district 
for a wagon road between Grand Rapids and Gypsumville which 
is the present terminus of the Canadian Northern line traversing 
the region east of Lake Manitoba. 
Prominent cliffs have been developed in the Devonian lime- 
stone series in the northern part of the Lake Winnipegosis basin, 
rising sometimes 80 feet above the lake, but none of these have 
any considerable extension north and south. 
Since the early stages of the glacial epoch geologic processes 
in this region have acted chiefly in a constructive way, first 
through the deposition in the river valleys of vast quantities 
of glacial till, followed by the lake deposits of Lake Agassiz, and 
still later by the deposits of the relatively small successors of 
Lake Agassiz and by the waters of the Saskatchewan river. The 
blocking of the original lines of drainage, which were adjusted 
to the Winnipeg and Winnipegosis plains, by the drift of the 
Glacial period, left visible only some of the more conspicuous 
features of the original topography already mentioned. Over the 
glacial drift a mantle of lacustrine deposits, generally thin but 
sometimes heavy, was spread by the great sheet of water known 
as Lake Agassiz. This lake, shortly after the retreat of the ice, 
covered the country from the Cretaceous scarp west of Lake 
Winnipegosis to the hills of crystalline rock east of Lake Winni- 
peg and extended from Minnesota and South Dakota nearly 
to the Churchill river. 1 The gravel terraces marking the old 
shore-fines, spits, and bars of the various levels of this ancient 
lake form conspicuous topographic features locally. Tyrrell 
found the highest of these, on Duck mountain, to have a height 
1 Warren Upham, Geol. Surv., Can., Ann. Rep. 1888-89 (1890), Vol. IV, pt.E. pp. 1-2,56. 
Tyrrell, J. B., Geol. Surv., Can,, Ann. Rep. 1890-91 (1893) Vol. V, pt. E, pp. 1-235. 
GeoL Surv., Can., Ann. Rep. Vol. XIII, pt. F. 
Dowling, Geol. Surv., Can., Ann. Rep. Vol. XIII, pt. FF. 
Mclnnes, Wra., Geol. Surv.. Can., Mem. No. 30, 1913, pp. 125-127. 
