GLEN ROY, IN SCOTLAND. 
43 
circumstances connected with these knolls de¬ 
serving special notice. They frequently pre¬ 
sent the glacial marks only on one side, while 
the opposite side has all the irregularities and 
roughness of a hill-slope not acted upon by ice. 
It is evident that the polished side was the one 
turned towards the advancing glacier, the side 
against which the ice pressed in its onward 
movement, — while it passed over the other 
side, the lee side as we may call it, without 
coming in immediate contact with it, bridging 
the depression, and touching bottom again a 
little farther on. As an additional evidence 
of this fact, we frequently find on the lee side 
of such knolls accumulations of the loose ma¬ 
terials which the glacier carries with it. It 
is only, however, when the knolls are quite 
high, and abrupt enough to allow any rigid 
substance to bridge over the space in its de¬ 
scent from the summit to the surface below, 
that we find these conditions ; when the knolls 
are low and slope gently downward in every 
direction, they present the characteristic gla¬ 
cier-surfaces equally on all sides. This cir¬ 
cumstance should be borne in mind by all who 
investigate the traces of glacier-action; for 
