110 S. Y. WOOD, JT7N., AND F. W. HARMEK ON THE 



mentioned to us by Mr. "Whitaker, it probably extended further into 

 that county, though now probably mostly removed by the inter- 

 glacial denudation which we have been discussing. Reviewing the 

 whole case, however, it seems to us that the evidence shows that 

 though Norfolk and Suffolk appear, with the exception of the ex- 

 treme northern part, near Cromer (where the Contorted Drift, capped 

 irregularly by the Middle Glacial, exclusively forms the country), 

 to be occupied almost entirely by the Upper and Middle Glacial 

 deposits, yet that this appearance is in a measure deceptive, and 

 that the chief portion of all this area is underlain by a continuation 

 of the Contorted-Drift deposit of North Norfolk more or less denuded 

 throughout its range, so as to form troughs wider and deeper than 

 the existing valleys, into which the succeeding Middle and Upper 

 Glacial deposits have been bedded as well as spread like a mantle 

 over the rest of the denuded surface. For a general view of the 

 extent to which the Lower Glacial formation is exposed over the 

 eastern half of Suffolk and Norfolk, we refer to the map which ac- 

 companies our " Introduction " before referred to. 



The absence over the greater part of Essex of any traces of the 

 Lower Glacial deposits precludes any satisfactory inference as to 

 how far the valleys of that county may have been formed or modified 

 by interglacial denudation. The middle portion of the valley of the 

 Blackwater has its eastern side formed by an escarpment of London 

 clay, which is part of a series of concentric curved escarpments to 

 which that of the Chalk extending from Cambridgeshire to the Chil- 

 tern Hills belongs. As it is evident that all these concentric escarp- 

 ments had their inception in one disturbance, we may infer that, if 

 one of them can be shown to be Preglacial, the rest of the concentric 

 series are Preglacial also. The Upper Glacial clay lies up to that 

 one of the series which is formed by the Chalk, and shows that it 

 had originated prior to that clay. The Middle Glacial also in part 

 of Bedfordshire occurs in such a way as to indicate that at the time of 

 its deposition the chalk escarpment had acquired much of its present 

 configuration ; but the Lower Glacial beds do not occur anywhere 

 in such a position as to indicate whether they preceded the forma- 

 tion of these escarpments. It is, however, most probable that they 

 did not ; for these curvilinear concentric escarpments appear to have 

 originated in disturbances which upheaved and terminated the older 

 Tertiary formations ; and on this assumption the portion of the 

 Blackwater valley referred to seems to be of Preglacial origin. In 

 this part of the valley a bed of blue clay, full of chalk debris, and 

 undistinguishable from the Upper Glacial of the Eastern Counties, 

 was found, in sinking a well at Witham railway-station, to underlie 

 the Middle Glacial gravel*. Some years ago we found what ap- 

 peared to us to be the same bed, in the bottom of the valley, in 

 some brick-earth pits at Appleford Bridge, near Witham, where it 

 passed up, seemingly without any break, into sandy laminated brick- 

 earth, which was overlain by gravel resembling that of the Middle 

 Glacial so plentiful in the neighbourhood. As this exposure cor- 



* Geol. Mag. vol. v. p. 98. 



