472 PEOCEEDINGS OP THE GEOLOGICAL SOCIEXT. 



Suffolk, although we have good lists of special localities. That such 

 a division exists in Suffolk, both lithologicaUy and palseontologically, 

 there can be no doubt ; and that it is to some extent maintained 

 in Norfolk is probable. But in Norfolk it is not always easy to 

 show the lino of separation, and it becomes a question whether the 

 differences in the MoUiiscan fauna are not differences produced in 

 the fauna of one period by local conditions of sea-bed, depth, and 

 fresh waters. There is no doubt that the lower beds, both in Suf- 

 folk and Norfolk, are more-shallow-water deposits, and that, in the 

 latter county especially, they contain a large freshwater element ; 

 while the upper beds, with greater depth of water, show the Mol- 

 lusca less drifted, more in situ, and as having been under the influ- 

 ence of colder currents. 



Not only, however, do the upper and lower beds differ, as at 

 Bramerton, but the same division shows marked differences in dif- 

 ferent pits. Thus the lower bed in the pit east of the one on the 

 common has been named by Mr. Reeve the Scrobicularia-hedi, from 

 the abundance of that sheU, of which only one or two fragments 

 have been found on the same level in the adjacent pit, while Trophon 

 claihratus, Diplodonta astartea, and Tapes aureus have been found by 

 Mr. Eeeve in the former pit and not in the pit on the common. So 

 Cardium edule and Littorina liUorea are rare at Aldeby, but are very 

 common at Beccles (section of town well), while of the Cerithium 

 tridnctum, also common at Beccles, only one specimen has been 

 found at Aldeby. In the same way the fossils from the same beds 

 at Thorpe, Bramerton, Postwick, Coltishall, and Horstead present 

 marked differences of grouping and in relative numbers. So, as is 

 weU known on our own coasts at present, the distribution of the 

 MoUusca presents rapid variation. Amongst other instances, Mr. 

 Jeffreys states that the Tellina halthica abounds in Swansea Bay, 

 but that not a single specimen is to be found at Oxwich Bay, 

 only nine miles distant. It is possible, therefore, that the differences 

 found to exist throughout the Norfolk and Suffolk areas are more 

 or less dependent on these causes — that Thorpe (Suffolk), "Wangford, 

 Thorpe (Norwich), may represent old lines of coast or shingle-banks 

 in the old sea, while SizeweU, Southwold, Beccles, Aldeby, and 

 Bramerton may represent synchronous deeper- water deposits. Dif- 

 ference of depth is also probably the cause why the fauna of Aldeby 

 is so much richer than that of the upper division at Bramerton, and 

 why so many of the older CoraUine-Crag species reappear. I have 

 therefore, for the present, taken the two divisions together ; and this 

 gives the following resxdt : — 



Total number of species recorded in the Norwich Crag 179 



>_ Deduct land and freshwater species 24 



doubtful and varieties 16 



— _40 



139 



