
GLACIAL PHENOMENA AND SUPERFICIAL DEPOSITS. 263 
pies but a very narrow strip of the bottom of the valley, and winds often 
in the most tortuous manner from side to side of its level floor. It is 
usually the first idea of a traveller, that’a great river has occupied the 
"valley at some former time, and completely filled it. A little consider- 
ation, however, serves to modify this belief, and it is very generally found 
onexamination that the comparatively puny stream by reason of its tor- 
tuous character, is still in some places excavating and undermining the 
banks of the main valley. Evidence is also found of the constant change 
of the position of the stream in the flat valley bottom, and places may be 
seen, where the excavations of late years are being covered by a sod 
of grass. Given only time enough, and the formation of these great 
woughs in the prairie, is accounted for by forces still in operation. 
There are valleys, it is true, which do not show any erosion of their 
sides now going on, and in which the immediate hollow of the 
stream is deeply cut, and a condition of comparative equilibrium 
attained. Some of these, may require for their explanation a period 
of greater rain; but at a certain stage of developement, every valley 
is apt to fall into this state, if the flow of water be not actually 
increasing. 
608. The valley of the Souris River, gives some excellent illustrations. 
Near Wood End it is of an average width of about one fourth of a mile. 
The stream is quite small, and in summer barely runs from pool to pool, 
between the stones of its bed; yet it is found, that at afmost every convex 
bend, the banks are scarped and bare, and are year by year being under- 
mined. For about six miles, the river preserves the same character, and 
then joins, almost at right angles, a larger old valley, about a mile wide, 
in which there is no flow of water above the place of junction. Here, 
though there is abundant evidence of the changeable nature of the river 
bed, in the presence of lagoon-like ponds, the banks are comparatively 
ruinous, and covered with vegetation, and are seldom approached by 
the stream. 
609. The rivers are‘ proved to have frequently changed their 
courses, and great valleys occur in which little or no present waterflow 
takes place, but which may once have carried important streams, now 
diverted. Prof. Hind has shown that the South Saskatchewan probably 
flowed at a former period by the great valley now occupied by the 
Qu’ Appelle, and River That Turns, to the Assineboine.* If the part of 

* Assineboine and Saskatchewan Exploring Expedition, p, 24, 
