[5] 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._ [6] Edward Hull, Quart. Geol. Journ., vol. xxiv, p. 324, 1868. [7] Playfair, Illust. of Hutt. Theory, § 42. [8] Geol. Trans., second series. vol. v, p. 452. [9] Conybeare and Phillips Outlines, etc., p. 376. [10] Phillips, Geology, Lardner’s Cyclop., p. 41. [11] See Mammatt’s Geological Facts, etc., p. 90 and plate. [12] Hull, Quart. Geol. Journ., vol. xxiv, p. 318, 1868. [13] H. D. Rogers, Geol. of Pennsylvania, p. 897. [14] Edward Hull, Quart. Geol. Journ., vol. xxiv, p. 323. CHAPTER VI. DENUDATION Denudation defined. — Its Amount more than equal to the entire Mass of Stratified Deposits in the Earth’s Crust. — Subaërial Denudation. — Action of the Wind. — Action of Running Water. — Alluvium defined. — Different Ages of Alluvium. — Denuding Power of Rivers affected by Rise or Fall of Land. — Littoral Denudation. — Inland Sea-Cliffs. — Escarpments. — Submarine Denudation. — Dogger-bank. — Newfoundland Bank. — Denuding Power of the Ocean during Emergence of Land. Denudation, which has been occasionally spoken of in the preceding chapters, is the removal of solid matter by water in motion, whether of rivers or of the waves and currents of the sea, and the consequent laying bare of some inferior rock. This operation has exerted an influence on the structure of the earth’s crust as universal and important as sedimentary deposition itself; for denudation is the necessary antecedent of the production of all new strata of mechanical origin. The formation of every new deposit by the transport of sediment and pebbles necessarily implies that there has been, somewhere else, a grinding down of rock into rounded fragments, sand, or mud, equal in quantity to the new strata. All deposition, therefore, except in the case of a shower of volcanic ashes, and the outflow of lava, and the growth of certain organic formations, is the sign of superficial waste going on contemporaneously, and to an equal amount, elsewhere. The gain at one point is no more than sufficient to balance the loss at some other. Here a lake has grown shallower, there a ravine has been deepened. Here the depth of the sea has been augmented by the removal of a sandbank during a storm, there its bottom has been raised and shallowed by the accumulation in its bed of the same sand transported from the bank.