Illustrations of the Huttonian Theory of the Earth

by John Playfair

Note x. § 37.

The height above the level of the sea at which the marks of aqueous deposition are now found.

177. We have two methods of determining the minimum of the change which has happened to the relative level of the sea and land; or for fixing a limit, which the true quantity of that change must necessarily exceed. The one is, by observing to what height the regular stratification of mountains reaches above the present level of the sea; the other is, by determining the greatest height above that level, at which the remains of marine animals are now found. Of these two criteria, the first seems preferable, as the fact on which it proceeds is most general, and least subject to be affected by accidental causes, or such as have operated since the formation of the rocks. The results of both, however, if we are careful to select the extreme cases, agree more nearly than could have been expected.

178. The mountain Rosa, in the Alps, is entirely of stratified rocks, very regularly disposed, and nearly horizontal.[86] The highest summit of this mountain is, by Saussure's measurement, 2430 toises, or 14739 English feet, above the level of the sea, or lower than the top of Mont Blanc only by 20 toises, or 128 feet.[87] This is, I believe, the highest point on the earth's surface, at which the marks of regular stratification are certainly known to exist; for though, by the account of the same excellent mineralogist, Mont Blanc itself is stratified, yet, as the rock is granite, the stratification vertical, and somewhat ambiguous, it is much less proper than Monte Rosa for ascertaining the limit in question.

[86] Voyages aux Alpes, tom. iv. § 2138.

[87] Ibid. § 2135.

179. Again, in the new continent, we have an instance of shells contained in a rock, not much lower than the summit of Monte Rosa. This is one described by Don Ulloa, near the quicksilver mine of Guanca-Velica, in Peru. The height at which a specimen of these shells, given by Ulloa to M. Le Gentil, was found, was 2222 1/3 toises, or 14190 feet English, above the level of the seas.[88] This height agrees with the preceding, within 549 feet, a quantity comparatively small.

[88] See Hist. Acad. des Sciences, 1770. Phys. Générale, No. 7.

180. The last of the facts just mentioned is curiously commented on by Mr Kirwan. As he has proved, he says, that the mountains higher than 8500 feet were all formed before the creation of fish, it follows, that the shells found at Guanca-Velica, must have been carried there by the deluge.[89] Now, without objecting to the proof here referred to, (though it seems very open to objection,) it is sufficient to remark, that, if the shells at Guanca-Velica were carried there by the deluge, or any other cause that operated after the formation of the rock of which the mountain consists, they can make no part of that rock, but must lie, like other adventitious fossils, loose and detached on the surface, or at most externally agglutinated to the stone. This, however, is certainly not the fact; for, in the account just quoted, we read, that Don Ulloa told M. le Gentil, "qu'il avoit détaché ces coquilles d'un banc fort épais." This seems plainly to indicate, that the shells were included in a bed of rock; But, granting that the expression is a little ambiguous, on turning to the Mémoires Philosophiques of the same author, the difficulty is completely removed, and it is made evident, that these shells are in fact integrant parts of the rock. "On voit dans ces montagnes-là, (about Guanca-Velica, and particularly at that in which is the quicksilver mine,) des coquilles entières, petrifiées et enfermées au milieu de la roche, que les eaux de pluie mettent à decouvert. Ces coquilles font corps avec la pierre; mais malgré cela, on remarque que la partie qui fut coquille, se distingue par la couleur, la structure, la qualité de la matière de tout autre corps pierreux qui l'enferme, et du massif qui s'est fixé entre les deux ecailles,"[90] &c. He goes on to say, that one can distinguish marks of these shells having been worn, before they were included in the stone.

[89] Geol. Essays, p. 54.

[90] Mém. Philosophiques de Don Ulloa, Discours xvi. vol. i. p. 364.

181. Thus it appears, that whatever proof any fossil shell affords, that the rock in which it is found was formed under the sea, the same is afforded by the fossil shells of Guanca-Velica; and we are, therefore, perfectly entitled to conclude, that the relative level of the sea and land has changed, since the formation of the latter, by more than 14000 feet. The height assumed in § 37 is therefore much under the truth; and the water, for which the Neptunists must provide room in subterraneous caverns, might very well have been stated at more than a five-hundredth part of the whole mass of the earth.

Thus also the argument by which the Neptunists would connect the creation of fish with the beginning of the secondary mountains, falls entirely to the ground. Indeed, it is strange that Mr Kirwan should have supposed it possible, that the shells in question were loose and unconnected with the rock, and had continued so, ever since the deluge, in such elevated ground, where the torrents wear and cut down the mountains with unexampled violence, and have hollowed out Quebradas so much deeper and more abrupt than the glens or vallies among other mountains. He had not, I believe, seen the passage I have quoted from Ulloa; but the circumstances did not warrant the shells in question to be regarded as extraneous and adventitious fossils. A geologist should have known better than to suppose this possible. When we see Voltaire ascribing to accidental causes the transportation of those shells which he had been told were often found among the Alps, we can excuse in a Poet and a Wit, that ignorance of the facts in mineralogy, which concealed from him the extreme absurdity of his assertion; but when a Chemist or Mineralogist talks and reasons in the same manner, we cannot consider him as entitled to the same indulgence.