othing but a system of
aquatic plants and animals appear. A continent of this sort is not found
upon the globe; and such a constitution of things, in general, would
not answer the purpose of the habitable world which we possess. It is
therefore necessary to modify the surface of such a continent of land,
as had been formed in the sea, and produced, by whatever means, into the
atmosphere for the purpose of maintaining that variety of plants and
animals which we behold; and now we are to examine how far the
proper means for that modification is to be found necessarily in the
constitution of this world.

If we consider our continent as composed of such materials as may decay
by the influence of the atmosphere, and be moved by water descending
from the higher to the lower ground, as is actually the case with the
land of our globe, then the water would gradually form channels in
which it would run from place to place; and those channels, continually
uniting as they proceed to the sea or shore, would form a system of
rivers and their branchings. But this system of moving water must
gradually produce valleys, by carrying away stones and earthy matter
in their floods; and those valleys would be changing according to the
softness, and hardness, destructability or indestructability of the
solid parts below. Still however the system of valley and river would
be preserved; and to this would be added the system of mountains, and
valleys, of hills and plains, to the formation of which the unequal
wearing down of the solids must in a great measure contribute.

Here therefore it is evident, _first_, that the great system upon the
surface of this earth, is that of valleys and rivers; _secondly_, that
no such system could arise from the operations of the sea when covering
the nascent land; _thirdly_, that this system is accomplished by the
same means which, are employed for procuring soil from the decaying
rocks and strata; and, _lastly_, that however this system shall be
interrupted and occasionally destroyed, it would necessarily be again
formed in time, while the earth continued above the level of the sea.
Whatever changes take place from the operation of internal causes, the
habitable earth, in general, is always preserved with the vigour of
youth, and the perfection of the most mature age. We cannot see man
cultivate the field, without perceiving that system of dry land provided
by nature in forming valleys and rivers; we cannot st