w of the soil; but they merely retard,
they cannot wholly prevent. In proportion as the mountains are
diminished, the haugh, or plain, between them grows more wide, and also
on a lower level; but while there is a river running on a plain, and
floods produced in the seasons of rain, there is nothing stable in the
constitution of the surface of the land.

The theory of the earth which I propound is founded upon the great
catastrophes that can happen to the earth. It supposes strata raised
from the bottom of the sea and elevated into mountainous continents.
But, between the catastrophes, it requires nothing further than the
ordinary everyday effects of air and water. Every shower of rain, every
stream, participates in the dissolution of the land, and helps to
transport to the sea the material for future continents.

The prodigious waste of the land we see in places has seemed to some to
require some other explanation; but I maintain that the natural
operations of air and water would suffice in time to produce the effects
observed. It is true that the wastage would be slow; but slow
destruction of rock with gradual formation of soil is just what is
required in the economy of nature. A world sustaining plants and animals
requires continents which endure for more than a day.

If this continent of land, first collected in the sea, is to remain a
habitable earth, and to resist the moving waters of the globe, certain
degrees of solidity or consolidation must be given to that collection of
loose materials; and certain degrees of hardness must be given to
bodies which are soft and incoherent, and consequently so extremely
perishable in the situation in which they are now placed.

But, at the same time that this earth must have solidity and hardness to
resist the sudden changes which its moving fluids would occasion, it
must be made subject to decay and waste upon the surface exposed to the
atmosphere; for such an earth as were made incapable of change, or not
subject to decay, would not afford that fertile soil which is required
in the system of this world--a soil on which depends the growth of
plants and life of animals--the end of its intention.

Now, we find this earth endued precisely with such degree of hardness
and consolidation as qualifies it at the same time to be a fruitful
earth, and to maintain its station with all the permanency compatible
with the nature of things, which are not formed to remain unchangeable.