THE TWO GREAT SCULPTORS. 105 
1 Physiography,' drains in this way no less than one- 
seventh of the whole of England. All the rain which 
falls in Berkshire, Oxfordshire, Middlesex, Hertford- 
shire, Surrey, the north of Wiltshire and north-west 
of Kent, the south of Buckinghamshire and of Glou- 
cestershire, finds its way into the Thames; making 
an area of 6160 square miles over which every little 
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 earthy 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 
