assumed something like their present valley form. Up the valley of any
of the great rivers, as, for instance, that of the Rhône above the
lake of Geneva, we note successive terminal moraines which clearly
indicate stages in the retreat of the ice when for a time it ceased to
go backward, or even made a slight temporary readvance. It is easily
seen that on such occasions the stones carried to the ice front would
be accumulated in a heap, while during the time when day by day the
glacier was retreating the rock waste would be left broadcast over the
valley.

As we go up from the course of the glacial streams we note that the
successive moraines have their materials in a progressively less
decayed state. Far away from the heap now forming, and in proportion
to the distance, the stones have in a measure rotted, and the heaps
which they compose are often covered with soil and occupied by
forests. Within a few miles of the ice front the stones still have a
fresh aspect. When we arrive within, say, half a mile of the moraine
now building, we come to the part of the glacial retreat of which we
have some written or traditional account. This is in general to the
effect that the wasting of the glaciers is going on in this century as
it went on in the past. Occasionally periods of heavy snow would
refresh the ice streams, so that for a little time they pushed their
fronts farther down the valley. The writer has seen during one of
these temporary advances the interesting spectacle of ice destroying
and overturning the soil of a small field which had been planted in
grain.

It should be noted that these temporary advances of the ice are not
due to the snowfall of the winter or winters immediately preceding the
forward movement. So slow is the journey of the ice from the _névé_