Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/118

80 S. V. WOOD, JITN., AND F. W. HARMER ON THE geological mapping, and by the numerous inland sections which occur (so far as any remnants of the Contorted Drift can be traced), is entirely in accordance with the state of things thus disclosed by the Norfolk cliff, the interglacial denudation in question becoming greater southwards, so far as Norfolk is concerned, and the inter- glacial valleys excavated becoming deeper and deeper as this denudation increases, so that instead of forming troughs in the Lower Glacial beds only, as in the cliff-section, they are there cut through the Lower Glacial beds altogether, and down into the Pre- glacial floor, as we shall endeavour to show. Before doing this, however, let us see what light the coast-section of East Norfolk and Suffolk affords upon the subject. From the point where the Forest-bed ceases, east of Hasboro', the cliff is very low, and the Preglacial floor, being beneath the beach, cannot be seen. This district, however, is low and flat, and there are no valleys beyond slight depressions of a few feet ; and from Eccles to Winterton, a distance of 10 miles, there is no cliff at all. From "Winterton southwards, so far as the Lower Glacial beds occur (which is but slightly, owing to the interglacial denudation they have undergone), they show no indication of having been deposited in any of the valleys which the coast-line intersects ; for had they been so they would (notwithstanding that the Preglacial floor is below the beach, at an unknown depth and invisible) have exhibited a tendency to dip into those valleys ; but they do not exhibit any such tendency. As far south as Yarmouth the cliff is greatly ob- scured by blown sand ; but south of Yarmouth the Contorted Drift, denuded to a small thickness, shows itself horizontally at the base of the cliff, until that again becomes obscured. For a considerable distance inland of Yarmouth and to within about 4 miles of Nor- wich the Preglacial floor is concealed at an unknown depth beneath the waterline of the country, and the Middle and Upper Glacial deposits, dipping into the valley by reason of the interglacial denuda- tion of it which preceded them, conceal much of the Lower Glacial in that part. South of Lowestoft, along the coast-section, the Contorted Drift has been almost entirely denuded, and the Lower Glacial pebbly sands underlying it have suffered from the same cause so much as to occur but occasionally. Where they do remain, however, they maintain their horizontality, and so far confirm the general uni- formity of level which we believe the Preglacial floor to have possessed in this part. So complete, however, has been the denuda- tion of the Contorted Drift over the range of the Suffolk coast-section, that its former spread over this area would not have been suspected were it not for the thick outliers of it which remain far away in South Suffolk, and one or two nearer exposures of it inland that rise as bosses through the Middle Glacial sands which have been bedded around them. For the same reason its spread over the Ked- Crag area would be similarly unsuspected, inasmuch as, in all the numerous sections of the Red Crag and its associated unfossiliferous sands that are deep enough to show any formation resting on them,