364 Rev. W. B. Clarke on the Geological Structure 



With respect to Mr. Charlesworth's subdivision of the crag into two ages, I 

 fully agree, with a qualification of the word age. If that gentleman had said 

 different periods of the same era, I could find no difficulty in admitting the 

 justness of the classification, as not only the species but genera of shells are 

 differently grouped according to localities. The Norwich crag, I also admit, 

 differs from the Suffolk ; and, on the authority of Mr. Woodward, I may state, 

 that bowldered Suffolk shells occur in the beds at Thorpe. The corals of the 

 lower bed, I am of opinion, betoken a warmer climate ; and 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. 



I fully assent, also, to the observations brought forward by Mr, Charlesworth 

 in a paper read before the British Association at Bristol, on the mixed nature 

 of the deposits now forming on the coast of East Anglia, in which the fossil re- 

 mains of the adjacent cliffs are intermingled with the shells of existing species; 

 and I was acquainted with examples long before the reading of that paper. 



As to the necessity of separating the diluvium from the crag, there can 

 be no question. The gravel found in the latter, if carefully examined, will be 

 acknowledged to differ from regular diluvial gravel : its occurrence only be- 

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

 been often repealed there can be no doubt, for the beds of superficial gravel 

 of Suffolk and Dorsetshire are evidently not of one period ; and no one who has 

 studied gravel deposits accurately, can refuse to admit, that there have been 

 more than one occurrence of diluvial action, after the deposition of the tertiary 

 formations. In Norfolk, it is true, that crag is involved in the clay; but if this 

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

 the crag, it is most curious that a line of demarcation should actually exist be- 

 tween the districts in Suffolk, occupied by these deposits, and that the clay is 

 never found below or intermixed with the crag. Moreover, this diluvial clay 

 has been trticed not only into Norfolk, but into Cambridgeshire and Essex, 

 close up to me metropolis. In Suffolk the same line which bounds the London 

 clay bounds the diluvial. The only rational conclusion is, that during the crag 

 era, an extraordinary convulsion took place, which shook the whole country. 

 Diluvial clay and gravel occur in cavities in the crag on Alderton Common, 

 and near Stratford St. Mary's, at the sixtieth mile-stone from London. (Plate 

 XXXI., fig. 6.) 



Respecting the conchological history of the crag I offer no remarks ; partly 

 because it does not fall within my object in writing this paper, and partly be- 

 cause the notes, which I formerly made, have been lost. 



