And it is easy to
conceive how, under any less beneficent dispositions of their masses of
hill, the continents of the earth might either have been covered with
enormous lakes, as parts of North America actually are covered; or have
become wildernesses of pestiferous marsh; or lifeless plains, upon which
the water would have dried as it fell, leaving them for great part of
the year desert. Such districts do exist, and exist in vastness: the
_whole_ earth is not prepared for the habitation of man; only certain
small portions are prepared for him,--the houses, as it were, of the
human race, from which they are to look abroad upon the rest of the
world, not to wonder or complain that it is not all house, but to be
grateful for the kindness of the admirable building, in the house
itself, as compared with the rest. It would be as absurd to think it an
evil that all the world is not fit for us to inhabit, as to think it an
evil that the globe is no larger than it is. As much as we shall ever
need is evidently assigned to us for our dwelling-place; the rest,
covered with rolling waves or drifting sands, fretted with ice or
crested with fire, is set before us for contemplation in an
uninhabitable magnificence; and that part which we are enabled to
inhabit owes its fitness for human life chiefly to its mountain ranges,
which, throwing the superfluous rain off as it falls, collect it in
streams or lakes, and guide it into given places, and in given
directions; so that men can build their cities in the midst of fields
which they know will be always fertile, and establish the lines of their
commerce upon streams which will not fail.

Sec. 7. Nor is this giving of motion to water to be considered as confined
only to the surface of the earth. A no less important function of the
hills is in directing the flow of the fountains and springs, from
subterranean reservoirs. There is no miraculous springing up of water
out of the ground at our feet; but every fountain and well is supplied
from a reservoir among the hills, so placed as to involve some slight
fall or pressure, enough to secure the constant flowing of the stream.
And the incalculable blessing of the power given to us in most valleys,
of reaching by excavation some point whence the water will rise to the
surface of the ground in perennial flow, is entirely owing to the
concave disposition of the beds of clay or rock raised from beneath the
bosom of the valley into ranks of enclo