be made in the classroom. We want to make a model
stream and see what happens to little fragments of soil that fall into
it.

[Illustration: Fig. 53. Inland cliff. Salisbury Crags, Arthur's Seat,
Edinburgh]

Fix up the apparatus shown in Fig. 54. The small beaker A is to
represent the narrow mountain stream, the larger one _B_ stands for the
wide river, and the glass jar _C_ for the mouth of the river or the
sea. Run water through them; notice that it runs quickly through _A_,
slowly through _B_, and still more slowly through _C_: we want it to do
this, because the stream flows quickly and the river slowly.

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Now put some soil into _A_. At once the soil is stirred up, the water
becomes muddy, and the muddy liquid flows into _B_. But very soon a
change sets in, the liquid in _A_ becomes clear, and only the grit and
stones are left in the bottom: all the mud--the clay and the silt--is
washed into _B_. There it stops for a long time, and some of it will
never wash out. The liquid flowing into _C_ is clearer than that
flowing into _B_. If you keep on putting fresh portions of soil into
_A_ you can keep _B_ always muddy, although _A_ is usually clear. At
the end of the experiment look at the sediment in each beaker: in _A_
it is clear and gritty, in _B_ it is muddy. If you can get hold of
some sea water put some of the liquid from _C_ into it: very soon this
liquid clears and a deposit falls to the bottom, the sea water thus
acting like the lime water on p. 20.

[Illustration: Fig. 54. Model of a stream. In _A_, where the stream
flows quickly, the water is clear and the sediment free from mud. In
_B_, where it flows slowly, the water is turbid and the sediment muddy]

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The experiment shows us that the fine material washed away by a quickly
flowing stream is partly deposited when the river becomes wider and the
current slower, and a good deal more is deposited by the action of the
salt water when the river flows into the sea. The rock that crumbles
away inland is spread out on the bed of the river or at its mouth.

[Illustration: Fig. 56. The two sides of the river at the bend]

The river Stour at Wye showed all these things so clearly that I will
describe it; you must then compare it with a river that you know, and
see how far the same features occur. At the bridge the stream was
shallow and flowed quickly: the bottom was gritty and pebbly, free from
mud, and formed a safe place for