, it is still less pure. It
carries with it not only carbonic acid, but acids produced by
decaying vegetables--by the roots of the grasses and trees which grow
above; and they dissolve the cement of the rock by chemical action,
especially if the cement be lime or iron. You may see this for
yourselves, again and again. You may see how the root of a tree,
penetrating the earth, discolours the soil with which it is in
contact. You may see how the whole rock, just below the soil, has
often changed in colour from the compact rock below, if the soil be
covered with a dense layer of peat or growing vegetables.

But there is another force at work, and quite as powerful as rain and
rivers, making the soil of alluvial flats. Perhaps it has helped,
likewise, to make the soil of all the lowlands in these isles--and
that is, the waves of the sea.

If you ever go to Parkgate, in Cheshire, try if you cannot learn
there a little geology.

Walk beyond the town. You find the shore protected for a long way by
a sea-wall, lest it should be eaten away by the waves. What the
force of those waves can be, even on that sheltered coast, you may
judge--at least you could have judged this time last year--by the
masses of masonry torn from their iron clampings during the gale of
three winters since. Look steadily at those rolled blocks, those
twisted stanchions, if they are there still; and then ask yourselves-
-it will be fair reasoning from the known to the unknown--What effect
must such wave-power as that have had beating and breaking for
thousands of years along the western coasts of England, Scotland,
Ireland? It must have eaten up thousands of acres--whole shires, may
be, ere now. Its teeth are strong enough, and it knows neither rest
nor pity, the cruel hungry sea. Give it but time enough, and what
would it not eat up? It would eat up, in the course of ages, all the
dry land of this planet, were it not baffled by another counteracting
force, of which I shall speak hereafter.

As you go on beyond the sea-wall, you find what it is eating up. The
whole low cliff is going visibly. But whither is it going? To form
new soil in the aestuary. Now you will not wonder how old harbours
so often become silted up. The sea has washed the land into them.
But more, the sea-currents do not allow the sands of the aestuary to
escape freely out to sea. They pile it up in shifting sand-banks
about the mout