In our last lecture we saw that water can exist in three forms:--
1st, as an invisible vapour; 2nd, as liquid water; 3rd, as solid
snow and ice.
To-day we are going to take the two last of these
forms, water and ice, and speak of them as sculptors.
To understand why they deserve this name we must first consider
what the work of a sculptor is. If you go into a statuary yard
you will find there large blocks of granite, marble, and other
kinds of stone, hewn roughly into different shapes; but if you
pass into the studio, where the sculptor himself is at work you
will find beautiful statues, more or less finished; and you will
see that out of rough blocks of stone he has been able to cut
images which look like living forms. You can even see by their
faces whether they are intended to be sad, or thoughtful, or
gay, and by their attitude whether they are writhing in pain,
or dancing with joy, or resting peacefully. How has all this
history been worked out from the shapeless stone? It has been
done by the sculptor's chisel. A piece chipped off here, a
wrinkle cut there, a smooth surface rounded off in another place,
so as to give a gentle curve; all these touches gradually shape
the figure and mould it out of the rough stone, first into a
rude shape and afterwards, by delicate strokes, into the form of
a living being.
Now, just in the same way as the wrinkles and curves of a statue
are cut by the sculptor's chisel, so the hills and valleys, the
steep slopes and gentle curves on the face of our earth, giving
it all its beauty, and the varied landscapes we love so well,
have been cut out by water and ice passing over them. It is true
that some of the greater wrinkles of the earth, the lofty
mountains, and the high masses of land which rise above the sea ,
have been caused by earthquakes and shrinking of the
earth. We shall not speak of these to-day, but put them aside as
belonging to the rough work of the statuary yard. But when once
these large masses are put ready for water to work upon, then
all the rest of the rugged wrinkles and gentle slopes which make
the country so beautiful are due to water and ice, and for this
reason I have called them "sculptors."
Go for a walk in the country, or notice the landscape as you
travel on a railway journey. You pass by hills and through
valleys, through narrow steep gorges cut in hard rock, or
through wild ravines up the sides of which you can hardly
scramble. Then you come to grassy slopes and to smooth plains
across which you can look for miles without seeing a hill; or,
when you arrive at the seashore, you clamber into caves and
grottos, and along dark narrow passages leading from one bay to
another. All these - hills, valleys, gorges, ravines, slopes,
plains, caves, grottos, and rocky shores - have been cut out by
the water. Day by day and year by year, while everything seems
to us to remain the same, this industrious sculptor is chipping
away, a few grains here, a corner there, a large mass in another
place, till he gives to the country its own peculiar scenery,
just as the human sculptor gives expression to his statue.
Our work to-day will consist in trying to form some idea of the
way in which water thus carves out the surface of the earth, and
we will begin by seeing how much can be done by our old friends
the rain-drops before they become running streams.
Everyone must have noticed that whenever rain falls on soft
ground it makes small round holes in which it
collects, and then sinks into the ground, forcing its way
between the grains of earth. But you would hardly think that the
beautiful pillars in Fig. 24 have been made entirely in this way
by rain beating upon and soaking into the ground.
Where these pillars stand there was once a solid mass of clay and
stones, into which the rain-drops crept, loosening the earthly
particles; and then when the sun dried the earth again cracks
were formed, so that the next shower loosened it still more, and
carried some of the mud down into the valley below. But here and
there large stones were buried in the clay, and where this
happened the rain could not penetrate, and the stones
became the tops of tall pillars of clay, washed into shape by the
rain beating on its sides, but escaping the general destruction
of the rest of the mud. In this way the whole valley has been
carved out into fine pillars, some still having capping-stones,
while others have lost them, and these last will soon be washed
away. We have no such valleys of earth-pillars here in England,
but you may sometimes see tiny pillars under bridges where the
drippings have washed away the earth between the pebbles, and
such small examples which you can observe for yourselves are
quite as instructive as more important ones.
Another way in which rain changes the surface of the earth is by
sinking down through loose soil from the top of a cliff to a
depth of many feet till it comes to solid rock, and then lying
spread over a wide apace. Here it makes a kind of watery mud,
which is a very unsafe foundation for the hill of earth above
it, and so after a time the whole mass slips down and makes a
fresh piece of land at the foot of the cliff. If you have ever
been at the Isle of Wight you will have seen an undulating strip
of ground, called the Undercliff, at Ventnor and other places,
stretching all along the sea below the high cliffs. This land
was once at the top of the cliff, and came down by succession of
landslips such as we have been describing. A very great landslip
of this kind happened in the memory of living people, at Lyme
Regis, in Dorsetshire, in the year 1839.
You will easily see how in forming earth-pillars and causing
landslips rain changes the face of the country, but
these are only rare effects of water. It is when the rain
collects in brooks and forms rivers that it is most busy in
sculpturing the land. Look out some day into the road or the
garden where the ground slopes a little, and watch what happens
during a shower of rain. First the rain-drops run together in
every little hollow of the ground, then the water begins to flow
along any ruts or channels it can find, lying here and there in
pools, but always making its way gradually down the slope.
Meanwhile from other parts of the ground little rills are
coming, and these all meet in some larger ruts where the ground
is lowest, making one great stream, which at last empties itself
into the gutter or an area, or finds its way down some grating.
Now just this, which we can watch whenever a heavy shower of rain
comes down on the road, happens also all over the world. Up in
the mountains, where there is always a great deal of rain,
little rills gather and fall over the mountain sides, meeting in
some stream below. Then, as this stream flows on, it is fed by
many runnels of water, which come from all parts of the country,
trickling along ruts, and flowing in small brooks and rivulets
down the gentle slope of the land till they reach the big stream,
which at last is important enough to be called a river.
Sometimes this river comes to a large hollow in the land and
there the water gathers and forms a lake; but still at the lower
end of this lake out it comes again, forming a new river, and
growing and growing by receiving fresh streams until at last it
reaches the sea.
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.