a while what agent could possibly have produced either one or both
of these effects?

There is but one; and that, if you have been an Alpine traveller -
much more if you have been a Chamois hunter - you have seen many a
time (whether you knew it or not) at the very same work.

Ice? Yes; ice; Hrymir the frost-giant, and no one else. And if
you will look at the facts, you will see how ice may have done it.
Our friend John Jones's report of plains and bogs and a lake above
makes it quite possible that in the "Ice age" (Glacial Epoch, as
the big-word-mongers call it) there was above that cliff a great
neve, or snowfield, such as you have seen often in the Alps at the
head of each glacier. Over the face of this cliff a glacier has
crawled down from that neve, polishing the face of the rock in its
descent: but the snow, having no large and deep outlet, has not
slid down in a sufficient stream to reach the vale below, and form
a glacier of the first order; and has therefore stopped short on
the other side of the lake, as a glacier of the second order, which
ends in an ice-cliff hanging high up on the mountain side, and kept
from further progress by daily melting. If you have ever gone up
the Mer de Glace to the Tacul, you saw a magnificent specimen of
this sort on your right hand, just opposite the Tacul, in the
Glacier de Trelaporte, which comes down from the Aiguille de
Charmoz.

This explains our pebble-ridge. The stones which the glacier
rubbed off the cliff beneath it it carried forward, slowly but
surely, till they saw the light again in the face of the ice-cliff,
and dropped out of it under the melting of the summer sun, to form