x SUPPLEMENT TO THE CRAG MOLLUSCA. 



be the same as the sand 5' of the pit behind the church, containing the fossiliferous bed x, 

 the identity of the Chillesford with the Bramerton section fails ; and the idea forces itself 

 that the Fluvio- marine Crag of the Bramerton section, and its overlying sands, which 

 pass so uninteruptedly up into the Chillesford beds, are newer than even the Scrobicularia 

 Crag itself. 



It, however, appears to us the more probable alternative, that the sands marked ? are 

 not the Chillesford sands of the pit behind the church, but some later deposit ; probably 

 the Middle Glacial sand (8), which, in a pit only a furlong north of the church, occurs 

 under the Boulder clay (9). Figure XVII accordingly represents the section on this 

 hypothesis, and on the assumption that if a clear section were carried down from the 

 Chillesford clay of the pit behind the church into the Red Crag, it would disclose that unin- 

 terrupted passage of the formations into each other which is represented on the left side of 

 the figure ; the sands marked ? lying somewhat in the way suggested by the broken line. 



It is important to observe that while this probable conformity exists at Chillesford, 

 the Red Crag of Walton is clearly unconformable to the Chillesford beds which overlie it ; 

 the sands of those beds (5') lying on a very irregular surface of the Red Crag and rilling 

 up the depressions in it (see Section XXI) ; while both these sands and the laminated 

 clay (5") above them overlap the Crag on the south side, and rest there on the London 

 clay (see Section Q).' Nothing, therefore, can be clearer, we think, than that the Walton 

 Crag, so distinguishable by its fauna from the newer Red Crag beds 4" and 4"', had been 

 denuded before the Chillesford beds overspread it, and is quite disconnected from them. 



If the hypothesis presented in Section XVII is true, we see that the northern part of 

 the Red Crag area continued to receive accumulations up to and during the time when 

 the Eluvio-marine Crag was deposited ; and that from a depression which then set in, 

 the Eluvio-marine Crag gave place, through the sands shown in the Bramerton section 

 without symbol, to the marine deposit, x., of that place ; while the sandbank 

 deposit, 4", of the Chillesford section gave place through the beds 4'" to the same 

 overlying bed x ; the submergence carrying the sands 5', in which this bed x occurs, 

 over the Walton Crag. 



The other instances which exist of the Chillesford beds over the Red Crag area, such 

 as those on the eastern side of the Deben, opposite Woodbridge, do not afford any 

 section which would show their conformability, or the reverse, to the underlying Red 

 Crag ; but the appearances, as far as they go, all point there to an unconforraability. 

 How far the sands which, in some of the excavations for phosphatic nodule working, 

 seem to pass down into the Red Crag by thin seams of comminuted shell in their lower 

 part may belong to the Crag, it is difficult to say. They are not, we think, the Chillesford 



1 In Section Q this overlap is represented as existing at the northern end also ; but as the face of the 

 cliff is there obscured, this is uncertain. 



The bed x can be detected in Walton Cliff, but the shells are in too decayed a state for extraction 01 

 even recognition. 



