SALI S) CHO SIM OLOVIIN TSS. 87 
been swept away, as well as all that part of the rock which had been 
affected by the disrupting and decomposing effects of surface 
exposure. In all these respects, the correspondence between the 
deposits made by glacier ice and the drift seems complete. 
So too, if knobs or bosses of rock, large or small, chance to 
be discovered by the retreat of the ice, they may be seen to pos- 
sess the form of voches moutonnées, with one side worn more than 
the others, and that the side facing up the valley. Now and then 
the strie affecting the surface of these voches moutonnées may be 
seen to be deflected from their normal course down the valley, 
and to be bent round the bosses, showing that the elevation influ- 
enced the details of the movement which made the striz, without 
turning the striating agent out of its general course. 
It is sometimes possible to go back a short distance beneath the 
ice itself. The many caves made by natural and human agencies 
afford such opportunity. Under the ice one may often be for- 
tunate enough to see the contact of the glacier with its bed. 
Under favorable circumstances the lower part of the ice may be 
seen to be set with stones and with other materials of all grades 
of coarseness and fineness. The movement of the rock-shod ice 
is too slow to be sensible, but it is easy to see that if it move at all, 
no matter how slowly, it must powerfully corrade its bed. At 
the same time that the bed of the glacier is striated and polished, 
the stones in the bottom of the ice, themselves the graving tools, 
will suffer wear similar to that which they inflict. Not only this, . 
but if the different parts of the ice move at different rates the 
stones will rub one another during the movement. As they rub 
against one another, or as they rub against the bed over which 
the ice is moving, flat surfaces as well as striations will be devel- 
oped. If for any reason the stones turn in their ice-setting, as 
when they encounter a resistant object in the rock-bed, they may 
expose a new surface to planation and striation, or the old surface 
may be lined in a new direction, thus developing a second set of 
striations crossing the first. If any particular stone is turned fre- 
quently enough and rubbed hard enough against its neighbors, or 
against the glacier’s bed, successive sets of striae may be effaced. 
