PLIOCENE PERIOD Df ENGLAND. 459 



to the sands of the latter. On the north side of this remnant (the 

 upper part of which consists of hard rock) the Eed Crag assumes the 

 fluvio-marine condition, which it maintains thence to its furthest 

 northern extremity in Sheet 68. Of this, the lowest portion, i. e. the 

 part precisely synchronous with the lowest beds of Butley, Boyton, 

 and Chillesford, occurs only at Thorpe, near Aldborough, in the south 

 of Sheet 49, in wells in the south-east of 50, and at Bramerton in the 

 centre of 66. 



^Further depression then took place over this northern area, ac- 

 companied probably with further elevation of the southern. This 

 carried the head of the estuary from Bramerton up to Aylsham, in 

 Sheet 68, and also submerged the Coralline-Crag remnant which 

 divided the fluvio-marine from the marine area — ^the result being 

 that a sheet of laminated micaceous clay was deposited over both the 

 flavio-marine portion of the E,ed Crag and that part of the marine por- 

 tion which was latest accumulated, viz. that of Butley and its neigh- 

 bourhood, as well as over the Coralline Crag which divided the two 

 areas. This sheet of clay having been first observed at Chillesford, 

 where it overlies this newer part of the Eed Crag, has gone by the 

 name of the Chillesford Clay ; and where either marine (as at Butley 

 and Chillesford) or fluvio-marine conditions (as at Bramerton) had 

 preceded it, this clay is separated from the Crag by sands. In the 

 marine area at Chillesford these sands, horizontal in their upper 

 part, gradually assume the oblique or foreshore character towards 

 their base as they graduate into the highly oblique red foreshore 

 Crag there. In their central portion these are full of valves of the 

 estuarine mollusk Scrobicularia jpi^erata, all detached ; but in their 

 upper layers, just under the clay, they contain the remains of Mol- 

 lusca preserved by the tranquil accumulation of sediment afforded 

 by deeper water, so that both valves of the Lamellibranchiata are 

 united. Conditions exactly analogous prevail at Bramerton ; for 

 there the fluvio-marine Crag is overlain by sands of similar thickness 

 to those with Scrobicularia at Chillesford ; and in them at one of the 

 Bramerton excavations that shell is common. These beds at Bra- 

 merton are succeeded by further sands just under the clay, and con- 

 taining a bed of shells corresponding to the tranquilly preserved bed 

 at Chillesford ; and in this fluvio-marine conditions can scarcely be 

 detected. 



Between Bramerton and Aylsham this laminated clay not only 

 becomes thin and more sandy, but the sands beneath it diminish 

 much in thickness, and there is no fluvio-marine bed divided by sands 

 from a more marine one as at Bramerton, but a fluvio-marine one 

 only; and in my view this part of the Crag represents only the 

 sediment of the estuary after it had, by the depression of its head, 

 been pushed back northwards, and the Bramerton part of it had 

 become marine, while the Butley foreshore had become submerged. 



While the Chillesford sand and clay are thus the uninterrupted 

 continuation, by slight submergence, of the fluvio-marine Crag of 

 Bramerton and Thorpe by Aldborough, and of that newest portion 

 of the marine Crag, they are not so of the oldest. As already men- 



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