Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/116

78 78 S. V. WOOD, JT7N., AND F. W. HAEMER ON THE Chillesford Clay and the Contorted Drift were removed by one and the same denudation, no evidence has as yet been found to determine, because none of the sections in these outliers of the Contorted Drift have been carried sufficiently deep to disclose it. The thickness of this Drift in one of the outliers, at Kesgrave, section XX. (page 104), would appear, from the well sunk below the bottom of the excava- tions made for brickmaking, to exceed 50 feet; but it is not unlikely that the lowest portion of this may be the Chillesford Clay, because, this Clay being equally a brick- earth with the Contorted Drift, there would be nothing to indicate in the workmen's report of a well- sinking its separate existence from the brick-earth of the Contorted Drift which overlay it. If therefore the Chillesford beds do remain anywhere over the area bounded by the Butley creek and the Stour, it is probable that they do so in the way suggested in sections XX. and XXI. (pp. 104, 105), carried through the Contorted-Drift outliers for the purpose of showing the unconformity between the Lower and Middle Glacial deposits which it is the principal object of this paper to describe ; in which case it seems probable also that they were removed by the denudation which destroyed so much of the Con- torted Drift and gave rise to the unconformity in question. 2. The Unconformity between the Lower and Middle Glacial, and the Interglacial Valley -excavation which is connected therewith. In reference to this unconformity we observed, at page xx of the before-mentioned "Introduction," u that the breaking off of this deposit (the Contorted Drift) into outliers southward is evidently due to a great denudation of the Lower Glacial formation prior to the accumulation of the Middle Glacial sands, which occupy to a great extent troughs or valleys in the Lower Glacial beds ; and that it is quite possible that outliers of it may be concealed under the table- lands of Middle Glacial sand which separate the East- Anglian valleys from each other ; " and we added that "it was clear that the valley- system of East Anglia had its inception in that denudation." The existence of this unconfornity in the Glacial series, and of this interglacial excavation of the East- Anglian valley-system, is of more general importance, geologically, than at first sight appears — because, if it were due to a conversion of the area into land after a considerable submergence had occurred giving rise to the Lower Glacial deposits, it indicates an arrest and reversal of the glacial subsidence which is not generally admitted, and has a bearing on one of the theories of climate which has lately provoked so much discussion. In entering upon this subject it will be convenient first to examine how far there is any indication of the valleys of Norfolk and Suffolk having had any existence prior to the deposit of the Glacial beds. Commencing with the long natural section afforded by the north coast of Norfolk, we find that while the surface of the country intersected by that coast is indented by deep valleys, an almost level floor of Chalk extends along the base of the cliff where these