he form of electricity, which may be
conveyed to great distances, it seems likely that our rivers will in
the future be a great source of national wealth.

We must turn again to river valleys, there to trace certain actions
less evident than those already noted, but of great importance in
determining these features of the land. First, we have to note that in
the valley or region drained by a river there is another degrading or
down-wearing action than that which is accomplished by the direct work
of the visible stream. All over such a valley the underground waters,
soaking through the soil and penetrating through the underlying rock,
are constantly removing a portion of the mineral matter which they
take into solution and bear away to the sea. In this way, deprived of
a part of their substance, the rocks are continually settling down by
underwear throughout the whole basin, while they are locally being cut
down by the action of the stream. Hence in part it comes about that in
a river basin we find two contrasted features--the general and often
slight slope of a country toward the main stream and its greater
tributaries, and the sharp indentation of the gorge in which the
streams flow, these latter caused by the immediate and recent action
of the streams.

If now the reader will conceive himself standing at any point in a
river basin, preferably beyond the realms of the torrents, he may with
the guidance of the facts previously noted, with a little use of the
imagination, behold the vast perceptive which the history of the river
valley may unfold to him. He stands on the surface of the soil, that
_debris_ of the rocks which is just entering on its way to the ocean.
In the same region ten thousand years ago he would have stood upon a
surface from one to ten feet higher than the present soil covering. A
million years ago his station would have been perhaps five hundred
feet higher than the surface. Ten million years in the past, a period
less than the lifetime of certain rivers, such as the French Broad
River in North Carolina, the soil was probably five thousand feet or
more above its present plane. There are, indeed, cases where river
valleys appear to have worked down without interruption from the
subsidence of the land beneath the sea to the depth of at least two
miles. Looking upward through the space which the rocks once occupied,
we can conceive the action of the forces in their harmonious
co-operation which have