from
the glacier to which they owe their origin encircling all those which
are nearer and nearer to it within the same glacial basin. And as no
glacier could reach to its farthest moraine without pushing forward all
the intervening loose materials, it is self-evident that the outer
moraines were first formed, and those nearer the glacier subsequently,
in the order in which they follow one another from the lower valleys to
the higher levels at which alone glaciers exist at present. Translating
these facts into words, we see that the glaciers to which these ancient
moraines owe their origin must have been retreating gradually while the
moraines were accumulating. But a glacier while uniformly retreating
forms no high walls of loose materials around its edges and at its lower
extremity; as it melts away, it only drops the burden of angular rocky
fragments which it carries upon its back over the loose fragments above
which it moves, and which it grinds to powder, or to sand, or to rounded
pebbles, in its progress. It is only where the glacier remains
stationary for a longer or shorter period that large terminal moraines
can accumulate; and they are generally found in such places in the
valleys of the Alps as would naturally determine the lower limit of a
glacier for the time being. There is no possibility of escaping the
conclusion that the ancient glaciers must have begun that series of
oscillations to which the accumulation of the moraines is to be
ascribed, at a time when ice-fields already occupied the whole area
which they have covered during their greatest extension. After we shall
have seen how many centres of dispersion of erratic boulders existed in
the northern hemisphere, similar to that of the Alps, we may perhaps be
able to form some idea of the manner in which these ice-fields
originated and gradually vanished.

Some investigators have been inclined to explain the presence of
boulders, moraines, drift, and the like phenomena, by the action of
water. But even if we could believe that rivers had brought along with
them such masses of rock, and deposited them where they are now found,
the regularity in the distribution of the materials disproves any such
theory. In the lateral moraines of the Lake of Geneva we have a striking
illustration of this apparently systematic division of the loose
materials; for the northeastern moraines of that glacial basin contain
rocks belonging exclusively to the northern side of t