buried in strata may
afford rock of such hardness that when the river comes to cross it it
forms a cascade, as at the Falls of the Ohio, at Louisville, Ky. It is
a characteristic of all other falls, except those first mentioned,
that they rarely plunge with a clean downward leap over the face of a
precipice which recedes at its base, but move downward over an
irregular sloping surface.

In the torrent district of rivers waterfalls are commonly very
numerous, and are generally due to the varying hardness in the rocks
which the streams encounter. Here, where the cutting action is going
on with great rapidity, slight differences in the resistance which the
rocks make to the work will lead to great variations in the form of
the bed over which they flow, while on the more gently sloping bottoms
of the rivers, where the _debris_ moves slowly, such variations would
be unimportant in their effect. When the torrents escape into the main
river valleys, in regions where the great streams have cut deep
gorges, they often descend from a great vertical height, forming
wonderful waterfalls, such as those which occur in the famous
Lauterbrunnen Valley of Switzerland or in that of the Yosemite in
California. This group of cascades is peculiar in that the steep of
the fall is made not by the stream itself, but by the action of a
greater river or of a glacier which may have some time taken its
place.

Waterfalls have an economic as well as a picturesque interest in that
they afford sources of power which may be a very great advantage to
manufacturers. Thus along the Atlantic coast the streams which come
from the Appalachian highlands, and which have hardly escaped from
their torrent section before they attain the sea, afford numerous
cataracts which have been developed so that they afford a vast amount
of power. Between the James on the south and the Ste. Croix on the
north more than a hundred of these Appalachian rivers have been turned
to economic use. The industrial arts of this part of the country
depend much upon them for the power which drives their machinery. The
whole of the United States, because of the considerable size of its
rivers and their relatively rapid fall, is richly endowed with this
source of energy, which, originating in the sun's heat and conveyed
through the rain, may be made to serve the needs of man. In view of
the fact that recent inventions have made it possible to convert this
energy of falling water into t