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But not only is the solid rock crumbling into soil by the action of air and water, but the soil gradually progresses towards the sea, and sooner or later the sea must swallow up the land. Vegetation and masses of solid rock retard the seaward flow 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.

Thus we have a view of the most perfect wisdom in the contrivance of that constitution by which the earth is made to answer, in the best manner possible, the purpose of its intention, that is, to maintain and perpetuate a system of vegetation, or the various races of useful plants, or a system of living animals, which are in their turn subservient to a system still infinitely more important—I mean a system of intellect. Without fertility in the earth, many races of plants and animals would soon perish, or be extinct; and with permanency in our land it were impossible for the various tribes of plants and animals to be dispersed over the surface of a changing earth. The fact is that fertility, adequate to the various ends in view, is found in all the quarters of the world, or in every country of the earth; and the permanency of our land is such as to make it appear unalterable to mankind in general and even to impose upon men of science, who have endeavoured to persuade us that this earth is not to change.