Whltaker — On Sulaerial Denudation. 449 



M. Cliarpentier also has expressed his belief ia the formation of 

 the valleys of the Pyrenees by their contained streams ;' and in later 

 times Colonel G-reenwood has taken up the subject and strongly de- 

 fended the Huttonian doctrine f Mr. Prestwich has treated of the 

 formation of valleys by the rivers flowing in them in the south-east 

 of Eagland and the north-west of France f Mr. Godwin-Austen of 

 the power of rain in the formation of deposits of loam, etc. (and 

 therefore in the destruction of something else beforehand) and of 

 the formation of Chalk valleys by " meteoric " actions ;* Professor 

 Kamsay, of the ploughing-out of lake-basins by glaciers and of the 

 denudation of the Weald f Professor Jukes, of the cutting-out of 

 certain valleys and escarpments by subaerial action ; ^ and M. 

 Ch. Martins, of the formation of some inland needles of rock by 

 weathering.'' 



Sir C. Lyell too has adopted the subaerial theory to a great extent, 

 as may be seen by the following, which he has kindly allowed me 

 to quote from a letter written shortly after this paper was read : — 

 " I have long ago modified my opinions on denudation, and I now 

 agree with you in considering that the escarpments round the Weald 

 are not inland cliffs, as I formerly supposed, although at some points 

 the sea may have entered through transverse valleys and modified 

 parts of them. Two arguments, namely the fact of the escarpment 

 of the Lower Greensand being parallel with that of the Chalk,* and 

 the fact that the sea cuts its cliffs successively through different forma- 

 tions and never keeps for such great distances to one formation only, 

 are I believe unanswerable." And with regard to the pinnacles and 

 needles of Chalk in the valley of the Seine (see p. 452), Sir Charles 

 continues : " Ever since I convinced myself that the sea had not 

 gone up the valley of the Somme farther than Abbeville, the highest 

 point at which mai'ine shells occur, I had great misgiving as to its 

 having been so effective as some eminent French geologists have 

 thought in excavating the valley of the Seine. Even if the sea, or 

 the rise and fall of the tide, extended as far as Eouen and further, I 

 cannot conceive its having gone up so far as to have made the pin- 

 nacles of Chalk near Andelys, without supposing a submergence in- 

 consistent with what we must infer respecting Picardy, which 

 appears, like the Wealden district, to have kept its head above water 

 during and since the Glacial Period." 



The following authors have also, in one way or another, supported 



1 Essai. sur la constitution geognostique des Pyrenees, 8vo., Paris, 1823, p. 25. 



2 Rain and Kivers, 8vo , Lond., 1857. Ed. 2 in 1866. 



3 Phil. Trans., vol. 154, p. 247; Quart. Journ. Geol. Soc, vol. xix. p. 497 (1863). 

 * Quart. Journ. Geol Soc, vol vi. p. 94 (1850); vol. vii. pp. 121-6, 13J, 131 



(1851); vol. xi. pp. 118, 119(1855); vol. xiii. pp. 63, 71 (1857). 



6 Ibid. vol. xviii. p. 1H5 (1862) ; Phil. Mag., vol. 28, p. 293 (1864) ; vol 29, p. 285. 

 (1865) ; The Physical Geology and Geography of Gt. Britain, 8vo., Loud. Ed. 2. 

 (1865). 



8 Brit. Assoc. Rept. for 1861, Trans, of Sections, p. 54 ; Quart. Journ. Geol. Soc, 

 wl. xviii. p. 378 (1862) ; Geol. Mag., vol. iii p. 232 (1866), vol. iv. p. 444. (1867). 



' Bull- Soc. Geol, France, 2 Ser., t. xii. p. 314 (1855J. 



8 I believe that Professor Ramsay started this argument against the marine origin 

 of escarpments. — W. "W. 



VOL. IV. NO, XL. 29 



