was
muddy, and seemed to stand still. But it was settling steadily, and at
one side the little river was found, flowing away with the water it drew
from the swampy, springy ground. All the mud was gone, now; the water
was clear. It flowed in a bed with a stony floor, and there were rough
steps where the water fell down in little sheets, forming a waterfall,
the first of many that make this river beautiful in the upper half of
its course. To get from the high level of that hillside spring to the
low level of the sea, the water has to make a fall of twenty-three
hundred feet, but it makes the descent gradually. It could not climb
over anything, but always found a way to get around the rocks and hills
that stood in its way. When the flat marsh land interfered, the water
poured in and overflowed the basin at the lowest margin.

In the rocky ground the two explorers found that the stream had widened
its channel by entering a narrow crevice and wearing away its walls. The
continual washing of the water wears away stone. Rocks are softened by
being wet. Streaks of iron in the hardest granite will rust out and let
the water in. Then the lime in rocks is easily dissolved. Every dead
leaf the river carried along added an acid to the water, and this made
easier the process of dissolving the limestone.

Every crumbling rock gives the river tools that it uses like hammer and
chisel and sandpaper to smooth all the uneven surfaces in its bed, to
move stumbling blocks, and to dig the bed deeper and wider. The steeper
the slope is, the faster the stream flows, and the larger the rocks it
can carry. Rocks loosened from the stream bed are rolled along by the
current. Then bang! against the rocks that are not loose, and often they
are able to break them loose. The fine sand is swept along, and its
sharp points strike like steel needles, and do a great work in polishing
roughness and loosening small particles from the stream bed. The bigger
pebbles of the stream have banged against the rock walls, with the same
effect, smoothing away unevenness and pounding fragments loose, rolling
against one another, and getting their own rough corners worn away.

The makers of stone marbles learned their business from a brook. They
cut the stone into cubical blocks, and throw them into troughs, into
which is poured a stream of running water. The blocks are kept in
motion, and the grinding makes each block help the rest to grind off the
eight corners a