324 PEOr. J. PRESTWICH ON THE EAISED 



Wealden area by earthquake-movements,^ and the spread of the 

 debris of those rocks by a great body of water flowing from that 

 centre over the adjacent lands. Subsequent research has shown 

 that this wide generalization cannot be admitted, that the larger 

 proportion of the Plint Drift in the valleys is to be attributed to 

 fluviatile action during late Pleistocene times, and that the drift on 

 the Chalk hills is even of still earlier date. Murcbison's paper, 

 which was marked by his usual power of observation and width 

 of grasp, has been the subject of sharp criticisms, but his critics 

 overlook the fact that he and Godwin-Austen were the first to point 

 out that there exist in the South of England certain flint-gravels, 

 the origin of which could be explained either by fluviatile or by 

 marine action. Murchison also showed that these rubble-beds 

 varied according to the distance from their source: that, while 

 angular and chalky in one place, they were worn and non-calcareous 

 in others, and sometimes passed into brick-earths. But it is im- 

 possible to accept the view that all the Flint Drift is due to one 

 sole cause — and that cause one of the nature described. On this 

 point, however, I have reason to know that Murchison's opinion was 

 subsequently much modified. 



Mr. F. Dixon, in a work of later date, expressed general agree- 

 ment with the opinion of Mantell, and remarked that the calcareous 

 rubble of the Elephant Bed of Brighton " shows every appearance 

 of having been spread out in successive horizontal layers by water 

 in motion," but without specifying in what manner or when this 

 was done.^ 



Sir Charles Lyell conceived that the materials of the Elephant 

 Bed of Brighton were " such as might have been heaped up above 

 the sea-level in the delta of a river draining a region of white 

 chalk," and that this delta might have been slowly subsiding while 

 the strata accumulated.^ He remarked also that the river and its 

 tributaries might have been occasionally frozen over, so that the 

 carrying power of ice co-operated with that of water to transport 

 fragile rocks and angular flints. In a later edition of his work 

 Sir Charles speaks of this calcareous rubble as probably contem- 

 poraneous with the similar rubble in the cliffs on the Norfolk coast. 



Mr. Pengelly considers the Head on the Devonshire coast to be 

 a subaerial accumulation of long growth, mainly derived from the 

 adjacent heights, and that it is not a mere talus,* to which some 

 geologists had likened it. 



By other geologists the accumulation of these and of analogous 

 beds has been ascribed to the action of ice and snow. The Eev. 0. 

 Fisher,^ speaking of the ' Trail,' remarks that it consists " of mate- 

 rials transported fropa higher grounds in rear, by some agent" which 



1 Of. cit. pp. 388 & 394. 



2 ' The Geology of Sussex,' 2nd ed. (1878) by Prof. T. Eupert Joues, p. 79. 

 ^ ' Manual of Elementary Geology,' 5th edit. (1855) p. 288, 



^ Trans. Devon Assoc, vol. ii. (1867) pp. 52-54. 



•5 Geol. Mag. for 1867, p. 193, and Quart. Journ. Gaol. Soc. vol. xxiu (1866) 

 p. 554. • 



