s, when reduced to
tillage, and where the rainfall is enough to maintain a good
agriculture, are, except when they have a coating of glacial waste,
exceedingly liable to destructive inundations.

Unhappily, the risk of river floods is peculiarly great in all the
regions of the United States lying much to the east of the Rocky
Mountains, except in the basin of the Great Lakes and in the district
of New England, where the prevalence of glacial sands and gravels
affords the protection which we have noted. Throughout this region the
rainfall is heavy, and the larger part of it is apt to come after the
ground has become deeply snow-covered. The result is a succession of
devastating floods which already are very damaging to the works of
man, and promise to become more destructive as time goes on. More than
in any other country, we need the protection which forests can give us
against these disastrous outgoings of our streams.

LAKES.

In considering the journey of water from the hilltops to the sea, we
should take some account of those pauses which it makes on its way
when for a time it falls into the basin of a lake. These arrests in
the downward motion of water, which we term lakes, are exceedingly
numerous; their proper discussion would, indeed, require a
considerable volume. We shall here note only the more important of
their features, those which are of interest to the general student.

The first and most noteworthy difference in lakes is that which
separates the group of dead seas from the living basins of fresh
water. When a stream attains a place where its waters have to expand
into the lakelike form, the current moves in a slow manner, and the
broad surface exposed to the air permits a large amount of
evaporation. If the basin be large in proportion to the amount of the
incurrent water, this evaporation may exceed the supply, and produce a
sea with no outlet, such as we find in the Dead Sea of Judea, in that
at Salt Lake, Utah, and in a host of other less important basins. If
the rate of evaporation be yet greater in proportion to the flow, the
lake may altogether dry away, and the river be evaporated before it
attains the basin where it might accumulate. In that case the river is
said to sink, but, in place of sinking into the earth, its waters
really rise into the air. Many such sinks occur in the central portion
of the Rocky Mountain district. It is important to note that the
pro