24 THIRD];SUPPLEMENT TO THE CRAG MOLLUSCA. 



terebra, Littorina littorea, Natica clama, Leda oblongoides, Lucina borealis, Cardium 

 edule, Astarte compressa, Cyprina islandica, Tettina obliqua, Corbula striata, and Mya 

 arenaria ; all being species which occur in the adjacent Crag beds. 



The fluvio-marine Crag from which the Chillesford beds have been removed to 'form 

 this channel, and on which the sands No. 6 thus rest below the beach line, comes through 

 the beach in two very small knobs about a quarter of a mile from the southern end of 

 Dunwich Cliff, which are crowded with shells ; and it yielded me also an equine tooth. 



Lastly, I have in the memoir of the " Newer Pliocene Period " in England, already 

 referred to, given rny reasons for regarding the Bridlington bed from which the Mollusca 

 given in the " Upper Glacial " column of the tabular list at the end of the first Supple- 

 ment to the " Crag Mollusca " were obtained, and also the basement clay of Holderness 

 with which that bed is associated, as being of Lower Glacial age, such clay being, in 

 fact, the actual moraine of the ice from which proceeded the material interstratified 

 in the Cromer Till (No. 6 a of the Map, &c.) ; and for regarding the molluscan 

 remains given in the "Middle Glacial" column of the same tabular list, as being 

 an admixture of remains from the bottom of some fiord which had been in pro- 

 cess of accumulation from the commencement of the sands No. 6, and during the 

 whole of the Glacial submergence, but which was ploughed out by the ice of the 

 chalky clay during its advance as it followed the retreating sea during emergence; 

 so that these remains became embedded by this derivative process in the upper part of 

 the Middle Glacial (No. 8 of the Map and Sections), as that bed was emerging, and 

 just before the chalky clay moraine was pushed over it. 



I should add that though, to avoid confusion in this explanation, I have adhered to 

 the term Middle Glacial, this formation is (in the view to which the continued study of 

 the subject has brought me) merely the marine accumulation which was synchronous with 

 the moraine of the land ice which is represented by the chalky clay ; and the precise 

 mode in which the two were accumulated, according to my view, is traced in detail in the 

 memoir just referred to.] 



