THE TWO GREAT SCULPTORS. 113 
longer in sinking, and lastly, the fine sand will be an 
hour or two in settling down, so that the water 
becomes clear. Now, suppose that this gravel were 
sinking in the water of a river. The stones would be 
buoyed up as long as the river was very full and 
flowed very quickly, but they would drop through 
sooner than the coarse sand. The coarse sand in its 
turn would begin to sink as the river flowed more 
slowly, and would reach the bottom while the fine 
sand was still borne on. Lastly, the fine sand would 
sink through very, very slowly, and only settle in 
comparatively still water. 
From this it will happen that stones will generally 
lie near to the bottom of torrents at the foot of the 
banks from which they fall, while the gravel will be 
carried on by the stream after it leaves the mountains. 
This too, however, will be laid down when the river 
comes into a more level country and runs more slowly. 
Or it may be left together with the finer mud in a lake, 
as in the lake of Geneva, into which the Rhone flows 
laden with mud and comes out at the other end clear 
and pure. But if no lake lies in the way the finer 
earth will still travel on, and the river will take up 
more and more as it flows, till at last it will leave this 
too on the plains across which it moves sluggishly 
along, or will deposit it at its mouth when it joins the 
sea. 
You all know the history of the Nile ; how, when the 
rains fall very heavily in March and April in the 
mountains of Abyssinia, the river comes rushing down, 
and brings with it a load of mud which it spreads out 
over the Nile valley in Egypt. This annual layer of 
