Theory of the Earth

when it will be found to have flowed, and to have been in fusion, by the operation of subterranean heat.

THIS evidence, though most conclusive with regard to the application of subterranean heat, as the means employed in bringing into fusion all the different substances with which strata may be found consolidated, is not directly a proof that strata had been consolidated by the fusion of their proper substance. It was necessary to see the general nature of the evidence, for the universal application of subterranean heat, in the fusion of every kind of mineral body. Now, that this has been done, we may give examples of strata consolidated without the introduction of foreign matter, merely by the softening or fusion of their own materials.

FOR this purpose, we may consider two different species of strata, such as are perfectly simple in their nature, of the most distinct substances, and whose origin is perfectly understood, consequently, whose subsequent changes may be reasoned upon with certainty and clearness. These are the siliceous and calcareous strata; and these are the two prevailing substances of the globe, all the rest being, in comparison of these, as nothing; for unless it be the bituminous or coal strata, there is hardly any other which does not necessarily contain more or less of one of other of these two substances. If, therefore, it can be shewn, that both of those two general strata have been consolidated by the simple fusion of their substance, no desideratum or doubt will remain, with regard to the nature of that operation which has been transacted at great depths of the earth, places to which all access is denied to mortal eyes.

WE are now to prove, first, That those strata have been consolidated by simple fusion; and, 2dly, That this operation is universal, in relation to the strata of the earth, as having produced all various degrees of solidity or hardness in these bodies.

I SHALL first remark, that a fortuitous collection of hard bodies, such as gravel and sand, can only touch in points and

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