It is foreign from the present purpose to enter on any history of the systems that, since the rise of this branch of science, have been invented to explain the phenomena of the mineral kingdom. It is sufficient to remark, that these systems are usually reduced to two classes, according as they refer the origin of terrestrial bodies to FIRE or to WATER; and that, conformably to this division, their followers have of late been distinguished by the fanciful names of _Vulcanists_ and _Neptunists_. To the former of these Dr Hutton belongs much more than to the latter; though, as he employs the agency both of fire and of water in his system, he cannot, in strict propriety, be arranged with either. In the succinct account which I am now about to give of this system, I shall consider the mineral kingdom as divided into two parts, namely, stratified and unstratified substances I shall treat, first, of the phenomena peculiar to the stratified; next, of those peculiar to the unstratified; and, lastly, of the phenomena common to both. Beginning, then, with the first, the subject naturally divides itself into three branches; viz. the _materials_ the _consolidation_, and the _position_ of the strata. SECTION I. OF THE PHENOMENA PECULIAR TO STRATIFIED BODIES. 1. _Materials of the Strata._ 1. IT is well known that, on removing the loose earth which forms the immediate surface of the land, we come to the solid rock, of which a great proportion is found to be regularly disposed in strata, or beds of determinate thickness, inclined at different angles to the horizon, but separated from one another by equidistant superficies, that often maintain their parallelism to a great extent. These strata bear such evident marks of being deposited by water, that they are universally acknowledged to have had their origin at the bottom of the sea; and it is also admitted, that the materials which they consist of, were then either soft, or in such a state of comminution and separation, as renders them capable of arrangement by the action of the water in which they were immersed. Thus far most of the theories of the earth agree; but from this point they begin to diverge, and each to assume a character and direction peculiar to itself. Dr Hutton's does so, by laying down this fundamental proposition, That in all the strata we discover proofs of the materials having existed as elements of bodies, which must have been destroyed before the formation of those of which these materials now actually make a part.[1] [Footnote 1: Hutton's Theory, vol. I p. 20, &c.]