250 
MR. PRESTWICH ON THE GEOLOGY OF THE DEPOSITS 
noticed the existence of terrace-gravels in the Thames valley, but explained them by 
alternate movements of depression and elevation'*. 
Sir ft. Murchison also described at length some of the Drift phenomena of the 
South-east of England, more especially of the Wealden area. This distinguished geolo- 
gist arrived at the conclusion that the heaps of detritus and angular debris following 
certain lines on the borders of the Wealden area, and found also in the Thames valley, 
result from the action of waves of translation passing from west to eastf, and that the 
fossil mammalia (at Folkestone) were destroyed “by violent oscillations of the land, and 
were swept by currents of water from their feeding-places into the hollows where we 
now find them”J. Mr. Hopkins, in reviewing the question of the Drift, agreed with 
Sir Roderick in supposing that the Wealden area has been traversed by waves of trans- 
lation §, and in attributing to such agencies much of the Drift phenomena. 
The observations of the distinguished naturalist the late Professor E. Forbes, 
recorded in his Anniversary Address, in 1854, to the Geological Society, express the 
then unsettled state of the question relating to the Drift |[ ; whilst the opinion hitherto 
commonly held with regard to the range in time of the large mammalia is manifested by 
Professor Phillips^]" and so many other eminent writers on the subject having restricted 
them to the preglacial period. 
In France similar differences of opinion have prevailed respecting these particular 
quaternary deposits. The views generally adopted, however, with regard to the valley- 
gravels have been that they are the result of diluvial action, caused by waves of transla- 
tion, or by cataclysms arising from the bursting of lakes, or by the sudden melting of 
the snow on mountain-chains. The deposits of this age in the valley of the Seine and 
other rivers in the North of France are usually classed under four divisions, viz. Loess , 
Diluvium rouge (part), Sables lacustres, and Diluvium gris, each being regarded as of 
separate and distinct origin, and the two diluviums referred to cataclysmic origin**. 
Thus there were two extremes ; I have been led to adopt an intermediate course. 
I could not admit the possibility of river-action, as it now exists, having in any length 
of time excavated the present valleys and spread out the old alluvia ; neither was it pos- 
sible to admit purely cataclysmic action in cases where the evidences of contempo- 
raneous old land-surfaces and of fluviatile beds were so common. But with river-action 
of greater intensity, and periodical floods imparting a torrential character to the rivers, 
the consequences of the joint operation are obtained, and the phenomena admit of 
* The occurrence of old river-terraces along narrow valleys is one of the features earliest noticed by geolo- 
gists, hut these are quite distinct from the great and isolated beds of gravel capping the adjacent hills. 
t Quart. Journ. Geol. Soc. vol. vii. p. 361. i Ibid. p. 386. § Ibid. vol. viii. p. li. || Ibid. vol. x. p. xliii. 
IT Manual of Geology, edit. 1855, p. 408. This opinion held good till 1859 and 1860. 
** An excellent resume of this subject is given in M. b’Archiac’s ‘ Progres de la Geologic,’ vol. ii. pp. 1-4, 
154-221, 421-433. See also Axsted’s ‘Elem. Course of Geol.’ 2nd edit. 1856, p. 416 et seq .; D’Omaeitts 
D’Hallot’s ‘Abrege de Geol.’ 7th edit. 1862, pp. 228-38, 449, 478; and a paper by M. Ch. d’Orbigny (fol- 
lowed by one by M. Leymerie) in Bull. Soc. Geol. 2 e ser. vol. xii. p. 1297-1304, with observations by 
M, Hebert and others ; and another by M. Butetjx in vol. xvii. p. 72. 
