114 Geological Society, 



With respect to Mr. Charlesworth's* subdivision of the crag into 

 two ages, the author fully agrees with a qualification of the word 

 age. If that gentleman had said different periods of the same age, 

 Mr. Clarke would find no difficulty in admitting the justness of the 

 classification j as not only species but genera of shells are differ- 

 ently grouped according to localities. The Norwich crag, he also 

 admits, differs from the Suffolk, and on the authority of Mr. Wood- 

 ward alludes to bouldered Suffolk shells occurring at Thorpe, in 

 Norfolk. 



The corals of the lower bed of the Suffolk crag, the author is of 

 opinion, betoken a warmer climate, and he says, if during the crag era 

 the earth gradually cooled, the change from a coralline deposit to one 

 more nearly related to the inhabitants of the present era, would be 

 the natural and inevitable result. 



Mr. Clarke fully assents to the observation brought forward by 

 Mr. Charlesworth in a paper, read before the British Association at 

 Bristolt } on the mixed nature of the deposits now forming on the coasts 

 of England, in which the remains of the adjacent cliffs are intermingled 

 with the shells of existing species ; and adduces examples with which 

 he was acquainted, long before the reading of that paper. 



The author then offers some further remarks on the necessity of 

 separating the diluvium from the crag. He is of opinion that the gravel 

 found in the latter, if carefully observed, will be acknowledged to dif- 

 fer from regular diluvial gravel, and that its occurrence only betokens a 

 diluvial action during the period of the crag. That such actions have 

 been often repeated, he says there can be no doubt, for the beds of 

 superficial gravel of Suffolk and Dorsetshire, are evidently not of the 

 same period; and no one who has studied gravel deposits accurately, 

 can refuse to admit, that there have been more than one diluvial 

 action, since the deposition of the tertiary formations. In Norfolk, 

 he adds, it is true, the crag is involved in the clay, but if this clay 

 which in that county is 400 feet and in Suffolk 300 feet thick, be one 

 with the crag, it is most curious that a line of demarcation should 

 actually exist, between the districts in Suffolk occupied by these de- 

 posits ; and that the clay is never found below or intermixed with the 

 crag. Moreover this diluvial clay has been traced not only into Nor- 

 folk but into Cambridgeshire and Essex, close up to the metropolis. 

 In Suffolk the same line which bounds the London clay bounds the 

 diluvial. By an extension of Mr. Lyeli's argument all diluvial depo- 

 sits, the author observes, might be included in the crag, and all other 

 formations considered as diluvial. The only rational conclusion in 

 Mr. Clarke's opinion, is, that during the crag era an extraordinary 

 convulsion took place which shook the whole country. He gives also 

 one or two instances in which diluvial clay and gravel have been in- 

 troduced into cavities in the crag from overlying beds of superficial 

 detritus. 



* Mr. Charlesworth's paper in which this division is established will be 

 found in Lond. and Edinb. Phil. Mag. vol. vii. p. 81 See also p. 464 of 

 the same volume, vol. viii. p. 529, and the paper referred to in the next note. 



t This paper appeared in L. and E. Phil. Mag. vol. x. p. 1. 



