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 study the rocks and solid strata of the earth, those bulwarks of the field and shore, without acknowledging the provident design of nature in giving as much permanency to our continent, as is consistent with sufficient fertility; and we cannot contemplate the necessary waste of a present continent, without perceiving the means for laying the foundation of another.  But the evidence of those truths is not open to a vulgar view; media are required, or much reasoning; and between the first link and the last, in this chain, what a distance, from the wasting of hard bodies upon the surface of the earth, to the formation of a solid rock at the bottom of the sea.

CHAP.  XIV.

Summary of the Doctrine which has been now Illustrated.

The system of this earth appears to comprehend many different operations; and it exhibits various powers co-operating for the production of those effects which we perceive.  Of this we are informed by studying natural appearances; and in this manner we are led to understand the nature of things, in knowing causes.