Illustrations of the Huttonian Theory of the Earth

by John Playfair

[200] La Place, ibid.

The other circumstance, on which the stability of our system depends, is the small eccentricity of the planetary orbits, or their near approach to circles. Were their orbits very eccentric, an opening would be given to progressive change, that might so far increase, as to prove the destruction of the whole. But neither the movement of all the planets in the same direction, nor the small eccentricity of their orbits, can be ascribed to accident, since that either of these should happen by chance, in as many instances as there are planets, both primary and secondary, is almost infinitely improbable. Again, that any necessity in the nature of things should have either determined the direction of the planetary motions, or proportioned the quantity of them to the intensity of the central force, cannot be admitted, as these are things unavoidably conceived to be quite independent of one another. It remains, therefore, that we consider the laws, which make the disturbances in our system correct themselves, and by that means give firmness and permanence to it, as a proof of the consummate wisdom with which the whole is constructed.

387. The geological system of Dr Hutton, resembles, in many respects, that which appears to preside over the heavenly motions. In both, we perceive continual vicissitude and change, but confined within certain limits, and never from a certain, mean condition, which is such, that, in the lapse of time, the deviations from it on the one side, must become just equal to the deviations from it on the other. In both, a provision is made for duration of unlimited extent, and the lapse of time has no effect to wear out or destroy a machine, constructed with so much wisdom. Where the movements are all so perfect, their beginning and end must be alike invisible.

Note xxi. § 122.

Changes in the apparent Level of the Sea.

388. In speaking of the natural epochs marked out by the phenomena of the mineral kingdom, we have supposed a greater simplicity, and separation of effects from one another, than probably takes place in nature. We have, for instance, abstracted, in speaking of the waste and degradation of the land, from that elevation which may have been carried on at the same time. This appeared necessary to be done, in order to simplify as much as possible the view that was to be given of the whole; but there can be no doubt, that, while the land has been gradually worn down by the operations on its surface, it has been raised up by the expansive forces acting from below. There is even reason to think, that the elevation has not been uniform, but has been subject to a kind of oscillation, insomuch, that the continents have both ascended and descended, or have had their level alternately raised and depressed, independently of all action at the surface, and this within a period comparatively of no great extent.

It will be easily understood, that the facts we are going to state, each taken singly, prove nothing more than a change of the line in which the surface of the sea intersects the surface of the land, leaving it uncertain to which of the two the change ought really to be ascribed. Taken in combination, however, these facts may determine what each of them separately cannot ascertain. I shall first, therefore, mention some of the principal observations relative to the change above mentioned, and shall then compare them, in order to discover whether it is most probable that this change has been produced by the motion of the land or of the sea.

389. If we begin with examining the coasts of our own island, we shall find clear evidence every where, that the sea once reached higher up upon the land than it does at present. The marks of an ancient sea beach are to be seen beyond the present limits of the tide, and beds of sea shells, not mineralized, are found in the loose earth or soil, sometimes as high as thirty feet above the present level of the sea. Some of these on the shores of the Frith of Forth are very well known, and have been often mentioned. Indeed, on the shores of that frith, many monuments appear, which would seem to carry the difference between the present and the ancient level of the sea, to more than forty feet. The ground on which the Botanic Garden of Edinburgh is situated, after a thin covering of soil is removed, consists entirely of sea sand, very regularly stratified, with layers of a black carbonaceous matter, in thin lamellæ, interposed between them. Shells I believe are but rarely found in it, but it has every other appearance of a sea beach. The height of this ground above the present level of the sea is certainly not less than forty feet.

390. On almost every part of the coast where the rocks do not rise quite abrupt and precipitous from the sea, similar marks of the lowering of the sea, or the rising of the land, may be observed. On the shores opposite to ours, the same appearances are remarked. The author of the Lettre Critique to M. de Buffon, tells us, that he had found the bottom of a bason at Dunkirk, which he had reason to think was dug about 950 years ago, ten feet and a half above the present low water mark, though it must have been originally under it. The bottom of this bason is in the native chalk. From this, the same author concludes, that the sea at Dunkirk lowers its level at the rate of an inch nearly in seven years. The observation was made in 1762, (Lettre à M. le Comte de Buffon, &c. p. 55.)[201]

[201] In the county of Suffolk, near Wood Bridge, at the distance of seven or eight miles from the sea, are the Crag-pits, in which prodigious quantities of sea shells are discovered, many of them perfect and quite solid, (Pennant's Arctic Zoology, Introd. p. 6.) Lincolnshire affords various proofs of the same kind; but some other circumstances in the appearance of that coast, just about to be taken notice of, indicate changes of a more complicated nature.