Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/133

Rh LATER TERTIAEY GEOLOGY OF EAST ANGLIA. 95 explanation in this view ; that of the Middle Glacial in the way attempted to be shown in the sequel of this paper ; and that of the Contorted Drift by its having been ploughed out up to that point by this great mass of glacier ice. The depth of the submergence which the structure of the Contorted Drift proves Northern Norfolk to have undergone during the Lower Glacial period renders it very difficult to suppose that the Fenland, and other low-lying country beyond it, did not participate in that submergence, and become covered with the Contorted Drift, unless their level has been greatly lowered since ; but if we assume that the land ice reached to this part at the com- mencement of the Middle Glacial, as explained in the sequel of the paper, it is easy to account for the great lowering of the level of these districts, as well as for the destruction of the Lower Glacial deposits over them, by the degradation of their somewhat soft strata which such ice must have effected. In whatever way, however, the valley of the Waveney and Little Ouse may have been excavated and brought to its present confluent character, it seems clear to us that it must have formed a channel or strait as the land rose out of the Upper Glacial sea, and that the tidal scour through it was, as in the case of the other East- Anglian valleys, the principal agent in its >*€-excavation. The valley of the "Waveney presents few exposures of the Contorted Drift ; but those that do occur seem to us sufficient to prove that this formation once spread in considerable thickness over the district through which the valley runs. The Middle Glacial, except where these remnants occur, occupies so uniformly the flank of the valley west of Beccles as to lead naturally to the inference that the valley was excavated out of this and the overlying Upper Glacial clay only, as represented by Mr. Prestwich in his well-known sections of the Hoxne bed *, and was thus of Postglacial origin. The presence of these remnants of the contorted drift, however, and the general structure of the valleys of East and Central Norfolk which we have been reviewing, appear to us to indicate that a much wider trough than that which the valley now forms was interglacially excavated in the Contorted Drift, and that the Middle Glacial overlain by the Upper Glacial was deposited in it. Moreover, at various points along the valley exposures of clay occur low down that are clearly either the bed a of Section V., or else the Upper Glacial clay of the high ground (No. 8), an instance of -which exists at Lopham, close to the source of the river — in either case proving interglacial exca- vation to some extent. A bed of clay with chalk debris exactly resembling the Upper Glacial and also the bed marked a in section IV. seems to underlie a great thickness of Middle Glacial sand in the cutting at Oulton two miles west of Lowestoft. The sloped and grassed condition of the cutting obscures the position of this bed relatively to the Middle Glacial sand through which the cutting is made ; and instead of this bed of clay underl}'ing the sand, it may be only a plunge of the Upper Glacial into it ; but if such underlie does occur, then this
 * Phil. Trar.s. I860, part ii. p. 304.