Vol. 56.] ME. E. W. HARMER Otf THE CRAO OF ESSEX. 723 



The commonest species of the Icenian zone are the following, 

 nearly three-fourths of them being recent, and nearly two-thirds 

 common North Sea forms : — 



Buccinum undatum. 

 Purpura lapillus. 

 Neptunea antiqua. 

 Ceritkium tricinctum. 

 Turritella incrassata. 



terebra. 



Littorina littorea. 

 Natica catena. 

 Beet en opercularis. 

 Nucula Cobboldice. 

 Leda oblong oides. 

 Lucina borealis. 



Cardium edule. 

 Astarte borealis. 



compressa. 



Cyprina islandica. 

 Tellina lata. 



Mactra ovalis. 



subtruncata. 



My a arenaria. 

 truncata. 



The presence at some localities in the Icenian area of a few land 

 and freshwater shells, 1 and of the estuarine species Scrohicularia 

 piperata, has been thought to point to estuarine conditions in East 

 Anglia during this period. The widespread area, however, which 

 these deposits cover and their great thickness in places, seem opposed 

 to such a view ; and notwithstanding that the general facies of the 

 fauna is more or less of an estuarine character, I am inclined to 

 think that these beds are marine, though accumulated near the 

 mouth of a river, possibly some tributary of the Rhine. 



While the Icenian Crag thus covers a larger district than the 

 Red Crag, and is in places of such great thickness, its character 

 is similar throughout, the only palseontological difference of any 

 importance by which the several beds can be divided being that the 

 arctic species Astarte borealis is distinctive of the northern part of 

 the area, for it is common near Norwich and in the Bure Valley, 

 less so in the north of Suffolk, while it is unknown farther south, as 

 at Aldeburgh, Bulchamp, Southwold, and Dunwich. Tellina lata 

 (calcarea) and some other northern forms are also rather more 

 abundant in the northern than in the southern part of the Icenian 

 area. 2 



The estuarine Chillesford Clay and underlying sand, always highly 

 micaceous, the latter containing at the pit behind Chillesford Church 

 a marine fauna still more boreal than that of the Icenian deposits, 

 which indicate a still farther northward retreat of the Crag sea and 

 an emergence of the East Anglian area, may be distinguished by 

 the term Chi lies fordian. The most characteristic fossils at the 

 Chillesford Church pit are : — 



Turritella terebra. 

 Natica catena. 

 Leda oblongoides. 



lanceolata. 



Nucula Cobboldice. 

 tenuis. 



Cardium edule. 



■ grxnlandicum. 



Mactra ovalis. 

 Tellina lata. 



obliqua. 



Mya truncata. 



1 Hence the former name of Fluvio- marine Crag for these beds. 



2 The upper bed at Bramerton has been generally reckoned much newer than 

 the lower one. There is, however, little difference between the two, except that 

 Leda. oblongoides, Astarte borealis and A. compressa are somewhat more common, 

 and land and freshwater shells less so in the upper than in the lower bed. 



3c2 



