22 ACROSS THE SUB-ARCTICS OF CANADA. 
here abrupt and precipitous, consisting of cut banks of 
stratified clay; in other places more receding, but by a 
gradual slope rising, beneath dense foliage, to an equal 
elevation. 
At this season of the year the water being high and 
the current swift, we made good time, covering a dis- 
tance of sixty miles for the first full day’s travel. About. 
noon on the 2nd, having reached a narrow part of the 
river, very remarkable massive walls of ice were found 
upon either bank, some distance above the water’s edge. 
These walls were of irregular thickness, and from eight. 
to ten feet in height ; but the most striking feature about. 
them was that they presented smooth vertical faces to 
the river, although built of blocks of every shape and 
shade from clear crystal to opaque mud. They extended 
thus more or less continuously for miles down the river, 
and had the appearance of great masonry dykes. The 
explanation of their existence is doubtless as follows: 
Earlier in the season the narrowness of the channel had 
caused the river ice to jam and greatly raised the water 
level. After a time, when the water had reached a 
certain height and much ice had been crowded up on the 
shores, the jam had given way and caused the water to. 
rapidly lower to a considerable extent, leaving the ice 
grounded above a certain line. Thus the material for 
the wall was deposited, and the work of constructing 
and finishing the smooth vertical face was doubtless per- 
formed by the subsequent grinding of the passing jam, 
which continued to flow in the deeper channel. After 
the passing of the first freshet, and the formation of 
these great ice walls, the water had gradually lowered 
to the level at which we found it. 
