elevations and apparently drifted into their present position by 

 the first rush of waters ; the second generally found at lower 

 elevations and apparently comminuted by the continued attri- 

 tion of the retiring waters." As he refers to this latter class of 

 deposits the gravels which are found between Cambridge and 

 Lynn, and which are clearly river-gravels of Post-glacial date, 

 it is evident that the Diluvial and Alluvial formations did not 

 accurately correspond with what are now known as the Glacial 

 and Post-glacial deposits. 



It is necessary to remember this while perusing the older 

 papers written on the subject ; and we may perhaps correlate 

 the old and new nomenclature as follows : — 



Dihivial ("Older division = Glacial Deposits. 



Detritus I Newer division = Older Valley -gravels. ] p , ., 



Alluvial Detritus = Newer Valley-gravels > -nw * -^ 



•' => Deposits, 



and Alluvium. J 



It soon began to be felt, however, that the formation of the 

 deposits grouped under the head of Diluvial Detritus could not 

 be attributed to one and the same set of agencies, and in his 

 Anniversary Address to the Geological Society in 1831, Prof. 

 Sedgwick observes that " we ought to have paused before we 

 adopted the Diluvian theory and referred all our old superficial 

 gravels to the action of the Mosaic flood.... Bearing upon this 

 difficult question there is I think one great negative conclusion 

 now incontestably. established — that the vast masses of diluvial 

 gravel scattered almost all over the surface of the earth do not 

 belong to one violent and transitory period." 



He apparently adopts the idea subsequently taken up by 

 De Beaumont, viz. that deluges were caused by the sudden 

 elevation of mountain-chains. De La Beche in 1834 takes the 

 same view, and accurately points out the probable northern 

 origin of the erratic blocks scattered over the north of Europe ; 

 he suggests that the elevation of the bed of the northern ocean 

 occasioned such a deluge, and adds — '" such waves (elsewhere 

 called waves of translatioyi) would necessarily tend to float 

 the northern glaciers with their usual burdens of blocks of 

 rock, lifting them to the southward \" 



^ Researches in Theoretical Geology, pp. 388, 389, 



