_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. [Footnote 86: Voyages aux Alpes, tom. iv. § 2138.] [Footnote 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. [Footnote 88: See Hist. Acad. des Sciences, 1770. Phys. Générale, No. 7.]