10

THEORIES OF THE EARTH.

EDWARD.

You mentioned, a little time ago, that Geology is a new science: now, I think that is strange, for philosophers must always have observed the appearances of mountains and valleys, and it is their business to explain, or at least endeavour to explain, whatever they observe.

MRS. R.

Yes; but philosophers, till within the last few years, were more anxious to go upon what they fancied, than upon what they saw; and to contrive systems and theories, than to examine facts; and the consequence was, that there were many Theories of the Earth, as they were called, but these cannot with much propriety be looked upon as Geology:-that, like other sciences, must be founded on fact.

EDWARD.

But there must have been some grounds, at least, for these theories of the earth-something plausible or interesting; otherwise nobody would have attended to them.

GEOLOGY, A NEW SCIENCE.

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MRS. R.

That I shall leave you to determine, after hearing the nature of a few of them. Burnet, the first of the theorists worthy of notice, says that, before the Deluge of Noah, the earth consisted of a light crust or shell, of uniform thickness, with the waters of the sea under it; that there were no mountains, no valleys, but one smooth unvarying surface over the whole earth; and that this crust, being broken up at the Deluge, formed the rocks and mountains as they at present exist.

EDWARD.

I think this is all very plausible, for it is said in Genesis, "that the fountains of the great deep were broken up!"

MRS. R.

But it is no where said that before the Deluge there were no rocks, mountains, nor valleys.

CHRISTINA.

If it was so, the earth must have looked a sad melancholy flat; Salisbury Plain is quite enough of such a landscape. Burnet, I should think, would have made a very sorry poet.

12

WOODWARD'S THEORY.

MRS. R.

On the contrary, his book is highly poetical, and is now read on that account alone. You may remark, that there could have been no rivers in this smooth mountainless world, for water cannot run unless there be a declivity.* Burnet, indeed, saw no use for water before the deluge, for there was no rain, he says, in these antediluvian times. I dare say, Edward, you will be more pleased with Woodward, whose theory undertakes to explain how shells became imbedded in marble and other rocks.

EDWARD.

That is precisely what I long so much to understand.

MRS. R.

Woodward says, the deluge was caused by all the solid parts of the earth dissolving and forming a paste, among which the sea-shells were mingled, by the agitation which then took place.

EDWARD.

But how were the rocks dissolved? I should

* See Conversations on Natural Philosophy, Conv. XI.

WOODWARD'S THEORY.

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like to know what it is that could destroy their cohesion.

MRS. R.

Woodward says that the powers of cohesion among minerals was suspended, so that their parts no longer adhered firmly together; but he has no other authority for this than his own fanciful conjectures: so, Edward, you must lay your account for a little disappointment; and, as you are fond of astronomy, I shall console you with an account of the theories of the earth derived, or partly derived, from it.

EDWARD.

I cannot perceive what connexion there can be between astronomy and the origin of rocks and mountains.

MRS. R.

Whiston, for example, supposed that the deluge was caused by the tail of a comet; Descartes and Leibnitz conceived that the earth was an old sun with its fire extinguished; and the celebrated naturalist, Buffon, fancied that a comet struck off a corner from our present sun, and this, being melted by heat, formed the earth, which is now gradually cooling.

14

THEORIES OF THE EARTH.

EDWARD.

I see nothing improbable in any of these theories. I think they seem to be very ingenious.

MRS. R.

You will admit, however, that ingenious as they seem, they are not supported by facts; and, in philosophy, we should not build systems on mere conjecture: such as that of De Marschall, who thinks all the rocks and the mountains have been produced by meteors, and have fallen at different times from the sky; and the shells in the marble being of different species from those of our present seas, he thinks, is an argument for their atmospheric origin.

EDWARD.

This seems to be very extravagant, indeed. I should like some more rational explanation.

MRS. R.

What would you think of the theory of Demaillet, who conjectures that the shell-fish themselves made the rocks, and that all animals, not excepting man, were inhabitants of the sea before