Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/146

108 S. V. WOOD, JTTN., AND F. W. HARMER ON THE between them, and occupying valleys interglacially denuded in the former in the manner already described ; for, with the exception of these few exposures, the sides of the Gipping valley are occupied by the Middle Glacial, like those of the Waveney. The valley of the Little Ouse and parts of the valleys of some of its tributaries are the only instances in Norfolk and Suffolk which, so far as we are aware, afford any indication of Preglacial origin. In this valley, about Thetford (as also in that of the Thet, a tributary of the Little Ouse), the Middle Glacial is not present, though it sets in higher up it to the eastward. A chalky deposit, very gritty, form- ing extremely light land, and much resembling in aspect the Con- torted Drift as it exists round Holkham, in North-west Norfolk, occurs within the slopes of the Thet and Little-Ouse valleys, as well as on the heights at and around Thetford ; but whether this is the Contorted Drift, or an abnormal form of the Upper Glacial, we have not been able to satisfy ourselves. There is also at the brick-kiln on the high ground about a mile north of Thetford a laminated brick-earth overlying a bed of marl or reconstructed chalk which rests on glaciated chalk, and which we have regarded as part of the Contorted Drift. It is possible, however, notwithstanding their not being confined to the valley, that this and the gritty deposit just referred to may represent the interglacial bed (a) of the Yare valley which we have already described and shown in sections Y. & VI. Further east, up the Little-Ouse valley, and near to the common source of that river with the Waveney, there occur some exposures of brick-earth that seem also to belong to the Contorted Drift. Of these one is 6 furlongs north by east of Garboldisham church, another about the same distance west of Knattishall church, and the third at Fen Street, Redgrave, the last of these being within the Waveney valley, whose source is a mile west of it. For this short distance, therefore, the Waveney valley is of Preglacial origin, like that of the Little Ouse. These three exposures of brick-earth are all within a valley which seems to have traversed a hill of chalk stretching north and south from the neighbourhood of Ixworth to that of East Harling, and which is now mostly covered by the Upper Gla- cial. Assuming this brick-earth to be the Contorted Drift, then that deposit, instead of covering a generally level floor, as it does to the eastward, here enters and lies in a valley of Preglacial origin, of which the Little-Ouse valley in this part is a re-excavation. Whether this valley was an estuary at the time of the deposition of the Contorted Drift, or merely a submarine channel, there is not evidence to show ; but in view of the very considerable submergence of Norfolk during the Lower Glacial period, which the dimensions of the marl masses that are imbedded in the Contorted Drift appear to indicate, an estuarine condition of the Little-Ouse valley during the deposition of that drift is difficult to understand. Two other small river-valleys occur in South Suffolk — that of the Brett, which flows by Hadleigh into the Stour, and that of the Box- ford, another tributary of the Stour. The country between these is occupied by a tableland of Upper Glacial clay, while along the