The River Thames, which you all know, and whose course
you will find clearly described in Mr. Huxley’s
‘Physiography,’ drains in this way no
less than one-seventh of the whole of England.
All the rain which falls in Berkshire, Oxfordshire,
Middlesex, Hertfordshire, Surrey, the north of Wiltshire
and north-west of Kent, the south of Buckinghamshire
and of Gloucestershire, finds its way into the Thames;
making an area of 6160 square miles over which every
rivulet and brook trickle down to the one great river,
which bears them to the ocean. And so with every
other area of land in the world there is some one
channel towards which the ground on all sides slopes
gently down, and into this channel all the water will
run, on its way to the sea.
But what has this to do with sculpture or cutting
out of valleys? If you will only take a glass
of water out of any river, and let it stand for some
hours, you will soon answer this question for yourself.
For you will find that even from river water which
looks quite clear, a thin layer of mud will fall to
the bottom of the glass, and if you take the water
when the river is swollen and muddy you will get quite
a thick deposit. This shows that the brooks,
the streams, and the rivers wash away the land as
they flow over it and carry it from the mountains down
to the valleys, and from the valleys away out into
the sea.
But besides earthly matter, which we can see, there
is much matter dissolved in the water of rivers (as
we mentioned in the last lecture), and this we cannot
see.
If you use water which comes out of a chalk country
you will find that after a time the kettle in which
you have been in the habit of boiling this water has
a hard crust on its bottom and sides, and this crust
is made of chalk or carbonate of lime, which the water
took out of the rocks when it was passing through
them. Professor Bischoff has calculated that the
river Rhine carries past Bonn every year enough carbonate
of lime dissolved in its water to make 332,000 million
oyster-shells, and that if all these shells were built
into a cube it would measure 560 feet.
Week 14
Imagine to yourselves the whole of St. Paul’s
churchyard filled with oyster-shells, built up in
a large square till they reached half as high again
as the top of the cathedral, then you will have some
idea of the amount of chalk carried invisibly past
Bonn in the water of the Rhine every year.
Since all this matter, whether brought down as mud
or dissolved, comes from one part of the land to be
carried elsewhere or out to sea, it is clear that
some gaps and hollows must be left in the places from
which it is taken. Let us see how these gaps are
made. Have you ever clambered up the mountainside,
or even up one of those small ravines in the hillside,
which have generally a little stream trickling through
them? If so, you must have noticed the number
of pebbles, large and small, lying in patches here
and there in the stream, and many pieces of broken
rock, which are often scattered along the sides of
the ravine; and how, as you climb, the path grows
steeper, and the rocks become rugged and stick out
in strange shapes.
