In this curious theory ttierefore we find some perception of 

 the true explanation, but obscured and distorted by the cata- 

 clysmal ideas which had so long obtained possession of men's 

 minds. The successive editions of Lyell's Principles of Geology 

 contributed greatly to remove the old and deep-rooted belief 

 in cataclysms and rushing waters, and to show how most 

 geological phenomena may be explained by the continued 

 action of agencies which are now actually operating in different 

 parts of the globe. 



The mistake of placing the older valley-gravels amongst the 

 Diluvial detritus began to be noticed. Lyell pointed out that 

 there might be Alluvia of various ages (see 4th Edition of 

 Principles, 1835, Vol. IV. p. 209), and he appears to use the 

 same term for denoting all superficial accumulations, to the 

 entire exclusion of Diluvium. 



The difficulty of distinguishing between the so-called 

 Diluvial and the older Alluvial detritus is commented upon 

 in Phillips's Guide to Geohgij, 2nd edition, 1835. 



In 1837 Dr Buckland withdrew his opinion regarding the 

 identity of the Diluvian epoch with the Noachiau deluge, 

 though he retained the term Diluvium and the idea of great in- 

 undations of water. After this recantation, however, the name 

 was gradually dropped, and the deposits began to be spoken of as 

 Drift or Northern Drift^ ; the theory of ice-agency was resus- 

 citated and finally adopted ; for the transporting power of 

 icebergs had been suggested long previously, and is mentioned 

 in Conybeare and Phillips' Geology (1822) as an attempted 

 though improbable method of accounting for travelled boulders. 



Our present knowledge of the Drift deposits has resulted 

 from a more careful examination of their distribution and 

 contents than had previously been undertaken ; — according to 

 Mr Trimmer^ it was Prof. Johnston about the year 1840 who 

 first called attention to the necessity for maps of the surface 

 geology, which should exhibit as he says "not only the limits 

 of the rocky formations, but also the nature and relative ex- 

 tent of the superficial deposits (Drifts) on which the soils so 

 often rest and from which they are not unfrequently derived." 



1 By Dr Mitchell for instance in 1838. P. G. S. iii. p. 3. 



2 Quart, Journ. Geol. Soc. Vol. vii. p. 37. 



