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]
[1] Hutton's Theory, vol. I p. 20, &c.
2. The calcareous strata are the portion of the mineral kingdom that gives the clearest testimony to the truth of this assertion. They often contain shells, corals, and other exuviæ of marine animals in so great abundance, that they appear to be composed of no other materials. Though these remains of organized bodies are now converted into stone or into spar, their shape and interior structure are often so well preserved, that the species of animal or plant of which they once made a part, can still be distinguished and pointed out among the living inhabitants of the ocean.
Others of the calcareous strata appear to be composed of fragments of some ancient rocks, which, after having been broken, have been again united into a compact stone. In these we find pieces clearly marked as having been once continuous but now placed at a distance from one another, and exhibiting exactly the same appearances as if they floated in a fluid of the same specific gravity with themselves.
From these, therefore, and a variety of similar appearances, Dr Hutton concludes, that the materials of all the calcareous strata have been furnished, either from the dissolution of former strata, or from the remains of organized bodies. But, though this conclusion is meant to be extended to all the calcareous strata, it is not asserted that every cubic inch of marble or of limestone contains in it the characters of its former condition, and of the changes through which it has passed. It may, however, be safely affirmed, that there is scarce any entire stratum where such characters are not to be found. These must be held as decisive with respect to the whole system of strata to which they belong; they prove the existence of calcareous rocks before the formation of the present; and, as the destruction of those is evidently adequate to the supply of the materials of these that we now see, to look for any other supply were superfluous, and could only embarrass our reasonings by the introduction of unnecessary hypotheses.[2]
3. The same conclusions result from an examination of the siliceous strata; under which we may comprehend the common sandstone, and also those pudding-stones or breccias where the gravel consists of quartz. In all these instances, it is plain, that the sand or gravel existed in a state quite loose and unconnected, at the bottom of the sea, previous to its consolidation into stone. But such bodies of gravel or sand could only be formed from the attrition of large masses of quartz, or from the dissolution of such sandstone strata as exist at present; for it will hardly be alleged, that sand is a crystallization of quartz, formed from that substance, when it passes from a fluid to a solid state.
Those pudding-stones in which the gravel is round and polished, carry the conclusion still farther, as such gravel can only be formed in the beds of rivers or on the shores of the sea; for, in the depths of the ocean, though currents are known to exist, yet there can be no motion of the water sufficiently rapid to produce the attrition required to give a round figure and smooth surface to hard and irregular pieces of stone. There must have existed, therefore, not only a sea, but continents, previously to the formation of the present strata.
The same thing is clearly shown by those petrifactions of wood, where, though the vegetable structure is perfectly preserved, the whole mass is siliceous, and has, perhaps, been found in the heart of some mountain, deep imbedded in the solid rock.
4. Characters of the same import are also found among the argillaceous strata, though perhaps more rarely than among the calcareous or siliceous. Such are the impressions of the leaves and stems of vegetables; also the bodies of fish and amphibious animals, found very often in the different kinds of argillaceous schistus, and in most instances having the figure accurately preserved, but the substance of the animal replaced by clay or pyrites. These are all remains of ancient seas or continents; the latter of which have long since disappeared from the surface of the earth, but have still their memory preserved in those archives, where nature has recorded the revolutions of the globe.