490 Whitaker — On Subaerial Denudation. 



from mass by its irresistible expansive power. That tbe slips take 

 place from the top is indeed well known, and good figures of one of 

 them have been given by Mr. Eedman.^ I have mj'^self seen a large 

 and fresh one, and noted the occurrence of a crop of wheat some way 

 down the slope. 



The coast from the Eeculvers westward for about two miles is of 

 a somewhat different character, by reason of the rise of the sandy 

 beds below the London Clay ; but still the waste of the cliff is from 

 the toj), masses of the clay being constantly thrown down to the foot. 

 The shajDe of the cliff is often different, the clay forming a slope at 

 the top and the sands a more or less vertical wall below. Another 

 agent too comes into play here — the wind, which when strong 

 blows away much of the fine loose sand (Oldhaven Beds^) next below 

 the London Clay. At Oldhaven Gap there is a well-marked cliff run- 

 ning inward from the shore at right angles, and with a broken slope 

 on the other (eastern) side. This " chine," which is about 300 yards 

 long, and the bottom of which is but little above high-water-mark, 

 has clearly been formed by land-water, although for the greater part 

 of the year the insignificant watercourse along it is quite dry, for the 

 sea has never touched its base, and I believe that it has been cut 

 farther inland within the memory of man. 



The sea, therefore, does not hy itself destroy the land, but is largely 

 helped by atmospheric actions. The former carries away what the 

 latter bring within its reach. Without the help of rain, frost, etc., 

 the sea would spend its force on compact and therefore on compara- 

 tively unyielding rocks : without the help of the sea these subaerial 

 forces would soon mask solid cliffs with slopes of debris, and thus 

 vastly decrease their own destructive power. The two destroying 

 powers working together in different ways, the sea horizontally 

 from below, the other set of agents vertically from above,^ cause ten- 

 fold the destruction of coast that either could do alone. 



Most observers indeed are more or less agreed as to the waste 

 of some cliffs from above, though so far as I know, this knowledge 

 of the power of surface-actions on the coast has not been applied to 

 the question of denudation. Sir C. Lyell indeed has said in his last 

 work, that " the waste of the cliffs by marine currents constitutes 

 on the whole a very insignificant portion of the denudation annually 

 effected by aqueous causes the action of the waves and cur- 

 rents on sea-cliffs, or their power to remove matter from above to 

 below the sea-level, is insignificant in comparison with the power of 

 rivers to perform the same task." * 



7. — Comparison between Cliffs and Escarpments. 

 From what has been remarked above therefore it is clear that 



^ Proc. Inst. Civ. Eng. vol. xxiii. p. 186, 1865, where, and in an earlier paper by 

 the same author (ibid. vol. xi. p. 162, 1854), the destruction of the South-east coast 

 of England is well treated of. 



^ Quart. Journ. Geol. Soc. vol. xxii. p. 412. 



3 See Jukes, Brit. Assoc. Rep. for 1862, Trans, of Sections, p. 61. 



* Principles of Geology, Ed. 10, vol. i. pp. 565, 570 (1867). 



