the
course of ages, the great aestuaries below London, Stirling, Chester,
or Cambridge.

It is river mud and sand. The river, helped by tributary brooks
right and left, has brought down from the inland that enormous mass.
You know that. You know that every flood and freshet brings a fresh
load, either of fine mud or of fine sand, or possibly some of it
peaty matter out of distant hills. Here is one indisputable fact
from which to start. Let us look for another.

How does the mud get into the river? The rain carries it thither.

If you wish to learn the first elements of geology by direct
experiment, do this: The next rainy day--the harder it rains the
better--instead of sitting at home over the fire, and reading a book
about geology, put on a macintosh and thick boots, and get away, I
care not whither, provided you can find there running water. If you
have not time to get away to a hilly country, then go to the nearest
bit of turnpike road, or the nearest sloping field, and see in little
how whole continents are made, and unmade again. Watch the rain
raking and sifting with its million delicate fingers, separating the
finer particles from the coarser, dropping the latter as soon as it
can, and carrying the former downward with it toward the sea. Follow
the nearest roadside drain where it runs into a pond, and see how it
drops the pebbles the moment it enters the pond, and then the sand in
a fan-shaped heap at the nearest end; but carries the fine mud on,
and holds it suspended, to be gradually deposited at the bottom in
the still water; and say to yourself: Perhaps the sands which cover
so many inland tracts were dropped by water, very near the shore of a
lake or sea, and by rapid currents. Perhaps, again, the brick clays,
which are often mingled with these sands, were dropped, like the mud
in the pond, in deeper water farther from the shore, and certainly in
stilt water. But more. Suppose once more, then, that looking and
watching a pond being cleared out, under the lowest layer of mud, you
found--as you would find in any of those magnificent reservoirs so
common in the Lancashire hills--a layer of vegetable soil, with grass
and brushwood rooted in it. What would you say but: The pond has
not been always full. It has at some time or other been dry enough
to let a whole copse grow up inside it?

And if you found--as you will actually find along some English
shores