with which the top is coated, just underneath the turf. What has
broken them up but frost? Look again, as stronger proof, at the
talus of broken stones--screes, as they call them in Scotland;
rattles, as we call them in Devon--which lie along the base of many
mountain cliffs. What has brought them down but frost? If you ask
the country folk they will tell you whether I am right or not. If
you go thither, not in the summer, but just after the winter's frost,
you will see for yourselves, by the fresh frost-crop of newly-broken
bits, that I am right. Possibly you may find me to be even more
right than is desirable, by having a few angular stones, from the
size of your head to that of your body, hurled at you by the frost-
giants up above. If you go to the Alps at certain seasons, and hear
the thunder of the falling rocks, and see their long lines--moraines,
as they are called--sliding slowly down upon the surface of the
glacier, then you will be ready to believe the geologist who tells
you that frost, and probably frost alone, has hewn out such a peak as
the Matterhorn from some vast table-land; and is hewing it down
still, winter after winter, till some day, where the snow Alps now
stand, there shall be rolling uplands of rich cultivable soil.

So much for the mechanical action of rain, in the shape of ice. Now
a few words on its chemical action.

Rain water is seldom pure. It carries in it carbonic acid; and that
acid, beating in shower after shower against the face of a cliff--
especially if it be a limestone cliff--weathers the rock chemically;
changing (in case of limestone) the insoluble carbonate of lime into
a soluble bicarbonate, and carrying that away in water, which,
however clear, is still hard. Hard water is usually water which has
invisible lime in it; there are from ten to fifteen grains and more