46 
THE PARALLEL ROADS OF 
accepted the glacial theory, were not wholly 
conversant with the mode of action of glaciers, 
that, in passing through the bottom of a valley, 
for instance, the glacier would take up large 
boulders, and, carrying them along with it, 
would push them up such a slope and deposit 
them on its summit. It is true that large 
boulders may sometimes be found in front of 
glaciers among the materials of their terminal 
moraines, and may upon any advance of the 
glacier be pushed forward by it. But I know 
of no example of erratic boulders being car¬ 
ried to considerable distances and raised from 
lower to higher levels by this means. All 
the angular boulders perched upon prominent 
rocks must have fallen upon the surface of 
the glacier in the upper part of its course, 
where rocky ledges rise above its surface and 
send down their broken fragments. The sur¬ 
face of any boulder carried under the ice, or 
pushed along for any distance at its terminus, 
would show the friction and pressure to which 
it had been subjected. In this connection it 
should be remembered that in the case of 
large glaciers low hills form no obstacle to 
their onward progress, especially when the 
