284 TRANSACTIONS OF THE CANADIAN INSTITUTE {[Vov. VIII. 
Mr. Oldham says, ‘‘that under a pressure of cohesion of its own 
substance 370 feet high, ice must yield and that no slow pressure greater 
than an equivalent to that depth of ice, could be transmitted by ice, 
while under a pressure of 960 feet of its own substance it would be crushed.” 
He then makes a careful estimate of the pressure required to excavate 
the Lake of Geneva and finds that it would require a pressure of nine 
miles of ice, to force a glacier en masse through and out of the lake. This 
is for solid ice, but with névé it would be little or nothing. Whymper 
says, ‘‘When water is in the form of a glacier, it has not the power of 
making concavities and working upon surfaces, which are not opposed 
to the direction of the current. It leaves marks that are readily dis- 
tinguished from those produced by torrent action. ‘The prevailing forms 
resultant from glacier action, are more or less convex. Ultimately all 
angles and almost all curves are obliterated and large areas of flat surfaces 
are produced and can be traced by means of bosses of rocks termed Rochés 
Moutonnées. They owe their peculiar form to the grinding of ice, but 
they were blocked, anterior to the formation of the glaciers, the hollows 
were not so much affected, but the eminences were ground down, the - 
depressions in modelling remained, but the parts in relief were taken 
away.” At several places in the Gérner glacier one can get underneath 
and see the ice bridging over hollows. When a glacier passes over 
rough ground, it is supported upon a number of points and bridges many 
hollows, the parts touched are alone abraded, while the hollows escape. 
The depressions which are not opposed to the direction of the glacier’s 
motion, if anything like perpendicular to it, remain and will continue 
to do so, becoming less and less, till the whole bed of the glacier has been 
reduced to a plane surface.’’ Such surfaces are common in Greenland 
and are called Rochés Nivelées. 
Prof. Niles in 1878 went a considerable distance under the Aletch 
glacier, saw a boulder through a tunnel of blue ice, which was continued 
as a deep furrow in the under surface of the glacier, for at least thirty 
feet from its beginning. As this was produced by the ice moving over 
and beyond the boulder, it was evident that the ice was moving more 
rapidly than the boulder. He saw other instances of the same kind and 
argues that the movement of boulders in a glacier is one of extreme slow- 
ness, even when compared with the motion of the glacier itself. Mr. 
Ball argues that ‘‘a glacier slides over concavities without touching them 
and applies all its grinding power to the convex portions of its bed, conse- 
quently valleys excavated by glaciers, should show a uniform model. 
Instead of this many of the Alpine valleys, consist of a series of level basins, 
rising in steps as we mount them and connected by gorges which are much 
narrower than the basins they link together. This is conclusive that 
