subsiding.[65-A] Whatever may have been the changes which the solid foundation underwent, whether accompanied by the melting, consolidation, crystallization, or desiccation of subjacent mineral matter, it is clear from the fact of the sea having remained shallow all the while that the bottom never sank down suddenly to the depth of many hundred feet at once. It is by assuming such reiterated variations of level, each separately of small vertical amount, but multiplied by time till they acquire importance in the aggregate, that we are able to explain the phenomena of denudation, which will be treated of in the next chapter. By such movements every portion of the surface of the land becomes in its turn a line of coast, and is exposed to the action of the waves and tides. A country which is undergoing such movement is never allowed to settle into a state of equilibrium, therefore the force of rivers and torrents to remove or excavate soil and rocky masses is sustained in undiminished energy. FOOTNOTES: [46-A] In the first three editions of my Principles of Geology, I expressed many doubts as to the validity of the alleged proofs of a gradual rise of land in Sweden; but after visiting that country, in 1834, I retracted these objections, and published a detailed statement of the observations which led me to alter my opinion in the Phil. Trans. 1835, Part I. See also the Principles, 4th and subsequent editions. [46-B] See his Journal of a Naturalist in Voyage of the Beagle, and his work on Coral Reefs. [46-C] See chapters xxviii. to xxxi. inclusive. [48-A] Edin. Trans. vol. vii. pl. 3. [50-A] Proceedings of Geol. Soc. vol. iii. p. 148. [53-A] See plan by M. Chevalier, Burat's D'Aubuisson, tom. ii. p. 334. [55-A] See M. Thurmann's work, "Essai sur les Soulevemens Jurassiques du Porrentruy, Paris, 1832," with whom I examined part of these mountains in 1835. [57-A] I am indebted to the kindness of T. Sopwith, Esq., for three models which I have copied in the above diagrams; but the beginner may find it by no means easy to understand such copies, although, if he were to examine and handle the originals, turning them about in different ways, he would at once comprehend their meaning as well as the import of others far more complicated, which the same engineer has constructed to illustrate _faults_. [60-A] Biographical account of Dr. Hutton. [60-B] See above, p. 49. and section. [60-C] Playfair, ibid.; see his Works, Edin. 1822, vol. iv. p. 81. [62-A] Playfair, Illust. of Hutt. Theory, Sec. 42. [62-B] Geol. Trans. second series, vol. v. p. 452. [64-A] Conybeare and Phillips, Outlines, &c. p. 376. [64-B] Phillips, Geology, Lardner's Cyclop. p. 41. [65-A] See the results of the "Geological Survey of Great Britain;" Memoirs, vols. i. and ii., by Sir H. De la Beche, Mr. A. C. Ramsay, and Mr. John Phillips. CHAPTER VI. DENUDATION.