Now
after it has been lying for some time, it will form a
crust on top which is sometimes the effect of wind pressure
and sometimes--under favourable conditions--of superficial
glaciation. A similar condensation takes place at the
bottom as the result of the work of gravity: a harder
core will form. Between the two there is layer upon layer
of comparatively softer snow. In these softer layers the
differences which are due to the stratified precipitation
still remain. And frequently they will make the going
particularly uncertain; for a horse will break through
in stages only. He thinks that he has reached the carrying
stratum, gets ready to take his next step--thereby throwing
his whole weight on two or at best three feet--and just
when he is off his balance, there is another caving in.
I believe it is this what makes horses so nervous when
crossing drifts. Later on in the winter there is, of
course, the additional complication of successive snowfalls.
The layers from this cause are usually clearly discernible
by differences in colour.
I have never figured out just how far I went along this
entirely unbroken road, but I believe it must have been
for two miles.
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