Page:VCH Suffolk 1.djvu/50

 A HISTORY OF SUFFOLK The lower portion, the main mass indeed which occurs beneath the Chillesford Clay, where that clay is present, is the more shelly portion, to which the name Icenian has been restricted by Mr. Harmer, and which he regards as the zone of Mactra subtruncata ; while the Chil- lesfordian stage he places as the zone of Leda oblongoides. The shelly beds of the Norwich Crag yield Cerithium tricinctum, Turritella terebra, T. incrassata. Purpura lapillus, Neptunea {Trophon) antiqua, Buccimim undatum, Littorina littorea, Cyprina islandica, Cardium edule, Mya arenaria, Tellina obliqua, T. prcetenius, T. lata, Pecten opercularis, Astarte borealis, Nucula cobboldia, fish remains such as Platax woodwardi, occasional coprolites, and bones and teeth of mastodon. The organic remains have been studied by Dr. W. M. Crowfoot of Beccles, Mr. E. T. Dowson of Geldeston and others. That the Norwich Crag was formed in shallow bays into which streams brought land and freshwater moUusca has been generally admitted. The Chillesford Clay itself has been regarded as of a more estuarine character, its laminated structure and the occurrence of re- mains of a cetacean to some extent supporting this view. The Chilles- ford fossils found in the sands beneath the clay at Chillesford are forms met with in the Norwich Crag, but on the whole the assemblage is regarded as rather more boreal in character than the lower or main portion of the Norwich Crag. The species include 'Turritella terebra, Natica catena, Leda oblongoides, Nucula cobboldice, Cardium edule and C. grcelandicum.^ Prestwich^ has recorded a number of shells from the Chillesford Clay at Easton Bavent, where however the clay is inter- bedded with much sand and shingle. The impersistence of the Chillesford Clay and its replacement by beds of sand and pebbly gravel are well-established facts. At Southwold we find the shelly gravel and sand of the crag at the north end of the cliff, with no representative of the Chillesford Clay ; and beds of this character, with occasional subordinate seams of clay, extend towards Westleton, where they are overlain by a newer group of pebbly gravels, which appear to be associated with the Middle Glacial Sands.^ Northwards we find below the Glacial Drift, along the Waveney valley near Somerleyton, some 20 feet of pebbly gravels ; and there are beds as far west as the Stantons, Bardwell and Wattisfield, which may be of Pliocene age. G. Maw noticed shelly gravel between Codden- ham and Crowfield, but there the shells were probably derived from Crag beds which are no longer preserved in situ* The Crag Series forms a water-bearing group, and where it rests on the London Clay or other Eocene clays water is held up and springs are thrown out. Where the Crag rests on Chalk the supply is modified by the relation to the plane of saturation in the Chalk, and by the local occurrence of the beds of Chillesford Clay. ' Proc. Geol. Assoc, xv. 440. * Geol. Mag. (1864), p. 295. 16
 * Hanner, ^art. Journ. Geol. Soc. Ivi. 721. - Ibid, xxvii. 345, +62.