U8 THE FAIRY-LAND OF SCIENCE. 
Running water is not only always carrying away 
mud, but at the same time laying it down here and 
there wherever it flows. When a torrent brings down 
stones and gravel from the mountains, it will depend 
on the size and weight of the pieces how long they 
will be in falling through the water. If you take a 
handful of gravel and throw it into a glass full of 
water, you will notice that the stones in it will fall to 
the bottom at once, the grit and coarse sand will take 
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 corh- 
paratively 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 
