116 S. V. WOOD, JITN., AND F. W. BARHER ON THE 



has since taken place. Of snch a change, however, we can 

 discover no indication, the great changes in relative level having 

 in our view occurred in that part of England which lies south of the 

 Thames, which was the theatre of disturbance at the close of the 

 Glacial period, when the country rose from the sea *. 



The explanation therefore which Mr. Penning has offered of the 

 absence of the Middle Glacial from the fens of Cambridgeshire, viz. 

 that the currents from the north that formed it were entirely ex- 

 cluded from the valley, seems to us altogether inadequate — because 

 its absence is not confined to that valley, but prevails over most 

 extensive districts, which must have become submerged by a depres- 

 sion of less than even 200 feet ; and the explanation is, we think, 

 rather to be sought in the position of the great branch of the land- 

 ice to which we have adverted. We may either suppose that the 

 original outspread of the Middle Glacial extended over this region, 

 and that the advance of the land-ice ploughed it out and destroyed 

 it along with much of the older formations on which it rested, or 

 that the land-ice occupied the region during the accumulation of 

 the Middle Glacial, and so prevented its deposit. It must be ad- 

 mitted that neither of these hypotheses explains the absence of the 

 formation beneath the Upper Glacial in South Essex, where this 

 for some miles overlaps it. It is also a perplexing feature that 

 some denudation has occurred in the bottoms of valleys, by which 

 the Upper Glacial (or clay un distinguishable from it) rests directly 

 on beds older than the Middle Glacial sand, as is shown in Section 

 XV. in the case of the Ket valley, and of which instances are also 

 to be found in the Waveney, Blyth, and Gipping valleys. This, if 

 the clay so occurring be the Upper Glacial, seems to have taken 

 place either during the accumulation of that deposit, or " that of the 

 Middle Glacial, but to have been very partial or local. We are not 

 prepared at present to offer any explanation of either of these 

 difficulties ; but, with this exception, the latter of the two hypo- 

 theses seems to harmonize with all the phenomena surrounding the 

 question, as we will endeavour to show. 



In a paper by one of us on the correlation of the Scotch and 

 English Glacial deposits f, the sequence of the Glacial formations 

 posterior to the Contorted Drift (that is, posterior to the interglacial 

 unconformity already discussed) was, it was attempted to be shown, 

 both vertical and horizontal, and much more the latter than the 

 former. In following the South- Yorkshire coast-section this is 

 clearly seen ; for the clay which near the Humber-mouth and for 

 some twenty miles north of it forms the lower part of the cliff, and, 

 as proved by borings, descends to a considerable depth beneath the 

 beach, is as full of rolled chalk as is the East>- Anglian Upper Glacial, 

 with which, indeed, we identify it. Where the Glacial beds remain 

 least denuded this clay is seen to be succeeded upwards (in sections 

 100 feet and more in height) by clay containing chalk debris in less 

 and less quantities, till in the uppermost portion of the cliff-section, 



* Quart. Journ. Geol. Soc. vol. xsxii. p. 198. 

 t Geol. Mag. April, 1872. 



