350 peoceEdin'gs op the geological society. 



The four Corals, the Bryozoa, and the Foraminifera found in the 

 Eed Crag must be looked upon with doubt in presence of its richer 

 neighbour the Coralline Crag, which has evidently contributed so 

 largely to its stock*. 



Mollusca. — Mr. Searles Wood describes in his monograph 239 

 species of shells. Of these he considers that 53 species are pro- 

 bably derived from the Coralline Crag, leaving 176 proper to the Red 

 Cragf. A certain number of these latter were formerly considered 

 to be extinct species; but the important researches in deep-sea 

 dredging carried on of late years by Mr. Gwyn Jeffreys and others have 

 shown that many of the species formerly supposed to be extinct 

 still exist in the deeper parts of the Atlantic and Mediterranean. 

 Many species, also, which were considered to be distinct are now 

 regarded as varieties. 



With a view to the modifications in the relations of the Eed-Crag 

 fauna to the recent one which these changes render necessary, 

 Mr. Jeffreys has kindly gone through the list I had tabulated from 

 Mr. Wood's monograph, added some new species, eliminated the 

 varieties, and identified the species found to be now living. 



On the question of the species which are to be considered ex- 

 traneous, there is still considerable difference of opinion. Mr. Jef- 

 freys justly states that "the question of which species may be 

 extraneous or derivative is at present in an unsatisfactory state." 

 It is a difficulty which has been felt by all observers, from Mr. 

 Charlesworth to Mr. Wood. For my own part I should be almost 

 disposed to regard the greater number of the species found in the 

 Crag of Suffolk and not in the Crag of Norfolk as derived from the 

 Coralline Crag. So large a proportion of the latter has been de- 

 stroyed, and, as it were, incorporated into the Eed Crag, that I can 

 conceive even certain species of the older deposit being now found 

 only in the newer one. It would, however, be too much to assume 

 such an origin for so large a proportion of these fossils. In the fol- 

 lowing Kst I have considered the fact of any species being found also 

 in the Norwich Crag a sufficient reason for removing it from the 

 list of extraneous fossils. As a rule I have also regarded the species 

 found at Walton $, together with those occurring in the Sables 



* Prof. Duncan has recently described (Geol. Soe. April 1871) a new coral 

 from the Eed Crag of Waldringfield, which he has named Solena&trma Prest- 

 wichii. 



t Mr. Wood now reduces the number of extraneous shells to 25 ; and Sir 

 Charles Lyell reestimates the extinct species as under : — 



Total Number. ^^^f^J^'' ^XSs'Jot''^ 



^ °^' known as living. 



Bivalves 128 31 ] 



Univalves 127 33 I 25 



Brachiopods 1 1 J 



(See ' Student's Elements,' p. 178.) 



\ The circumstance even of a fossil occurring at Walton does not exclude tlie 

 possibility of extraneous derivation ; for I have found fragments of thin lime- 

 stone from the Coralline Crag even thei*e. 



