larger ravines through which the run-off flows soon descend below
the ground-water surface. Here springs discharge along the sides
of the little valleys and permanent streams begin. The water
supplied by the run-off here joins that part of the rainfall which
had soaked into the soil, and both now proceed together by way of
the stream to the sea.

RIVER FLOODS. Streams vary greatly in volume during the year. At
stages of flood they fill their immediate banks, or overrun them
and inundate any low lands adjacent to the channel; at stages of
low water they diminish to but a fraction of their volume when at
flood.

At times of flood, rivers are fed chiefly by the run-off; at times
of low water, largely or even wholly by springs.

How, then, will the water of streams differ at these times in
turbidity and in the relative amount of solids carried in
solution?

In parts of England streams have been known to continue flowing
after eighteen months of local drought, so great is the volume of
water which in humid climates is stored in the rocks above the
drainage level, and so slowly is it given off in springs.

In Illinois and the states adjacent, rivers remain low in winter
and a "spring freshet" follows the melting of the winter's snows.
A "June rise" is produced by the heavy rains of early summer. Low
water follows in July and August, and streams are again swollen to
a moderate degree under the rains of autumn.