EXTERNAL APPEARANCE OF GLACIERS. 285 
subside and be dispersed ; and, indeed, these 
pyramids, which are often quite lofty, and yet 
look as if they would crumble at a touch, prove, 
on nearer examination, to be perfectly solid, and 
are, in fact, pyramids of ice with a thin sheet of 
sand spread over them. A word will explain 
how this transformation is brought about. As 
soon as the level of the glacier falls below the 
sand, thus depriving it of support, it sinks down 
and spreads slightly over the surrounding sur- 
face. In this condition it protects the ice imme- 
diately beneath it from the action of the sun. 
In proportion as the glacier wastes, this pro- 
tected area rises above the general mass and be- 
comes detached from it. The sand, of course, 
slides down over it, spreading toward its base, 
so as to cover a wider space below, and an ever- 
narrowing one above, until it gradually assumes 
the pyramidal form in which we find it, covered 
with a thin coating of sand. Every stage of this 
process may occasionally be seen upon the same 
glacier, in a number of sand-piles raised to va- 
rious heights above the surface of the ice, ap- 
proaching the perfect pyramidal form, or falling 
to pieces after standing for a short time erect. 
The phenomenon of the large boulders, sup- 
ported on tall pillars of ice, is of a similar char- 
acter. A mass of rock, having fallen on the 
surface of the glacier, protects the ice immedi- 
