nd the twelve ridges of each one. The water becomes muddy
with the fine particles, just as the drip from a grindstone becomes
unclean when an axe is ground. Pretty soon all the blocks in the trough
are changed into globes--the marbles that children buy at the shops when
marble season comes around.

I suppose if the troughs are not watched and emptied in time, the
marbles would gradually be ground down to the size of peas, then to the
size of small bird shot, and finally they would escape as muddy water
and fine sand grains.

Sure it is that the sandy shores that line most rivers are the remnants
of hard rocks that have been torn out and ground up by the action of the
current.

Not very many miles from its first waterfall the stream had grown so
large that my two friends knew that they would soon find their canoes.
The plan now was to float down the curious, winding river and to learn,
if the river and the banks could tell them, just why the course was so
crooked on the map. They came into a broad, level valley where streams
met them, coming out of deep clefts between the hills they were leaving
behind them. The banks were pebbly, but blackened with slimy mud that
made the water murky. The current swerved from one side to the other,
sometimes quite close to the bank, where the river turned and formed a
deep bend. On this side the bank was steep, the roots of plants and
trees exposed. On the opposite side a muddy bank sloped gently out into
the stream. Here building up was going on, to offset the tearing down.

The sharp bends are made sharper, once the current is deflected from the
middle of the stream to one side. At length the loops bend on each other
and come so near together that the current breaks through, leaving a
semicircular bayou of still water, and the river's course straightened
at that place. It must have been in a spring flood that this cut-off was
made, and, the break once made was easily widened, for the soil is fine
mud which, when soaked, crumbles and dissolves into muddy water.

Stately and slow that river moves down to the bay, into which it empties
its load. The rain that falls on hundreds of square miles of territory
flows into the streams that feed this trunk. The little spring that is
the headwater of the system is but one of many pockets in the hillsides
that hold the water that soaks into the ground and give it out by slow
degrees. Surface water after a rain flows quickly into the streams. I