6 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY, [NoV. 9 



"Wealden denudation is represented. In the gravel (which is com- 

 posed of chalk-flint, with a considerable percentage of quartzites) 

 there occur fragments of other rocks, among which are some of 

 chert, sandstone, and limestone, that may possibly belong to rocks 

 within the Weald, though I am not aware that such an origin can 

 be with any certainty affixed to them. Again, Mr. Prestwich men- 

 tions having found fragments of chert and ragstone that he refers to 

 the Lower Greensand of Kent in the shingle of the cUff near South- 

 wold, belonging to the Glacial formation. 



Such occurrences as these, however, afford no ground for conclu- 

 ding more than that prior to the Glacial epoch such a planing off of 

 the Wealden area had begun as to afford exposures of the beds 

 beneath the chalk, from which some fragments might at the com- 

 mencement of the glacial period have found their way into gravels 

 then in course of formation. The evidence necessary, however, to 

 justify any assumption that the Weald valley existed as a subaerial 

 tract during the whole Glacial period must go very far beyond this. 

 Whether we suppose this valley to have been occupied during the 

 Glacial period with ice which streamed through the lateral valleys 

 of the north-east side into the Thames area — or whether we suppose 

 it to have had a milder climate, so that rivers of water instead of ice 

 followed the same course — in either case great volumes of the wreck 

 of the subcretaceous strata ought to have been brought into the 

 glacial beds which approach so near to the Wealden area as do those 

 of the south of Essex ; but these beds, especially the Boulder-clay, 

 are conspicuous by their absence. If we consider through what various 

 beds of stone the Medway and Darent valleys are cut, and what 

 immense quantities of this stone must have been removed to form 

 them, the absence or extreme paucity of such debris in the Glacial 

 beds is significant ; but if we couple, as we have been asked to do, 

 the denudation of the great valley of the Weald itself with the ero- 

 sive action of the Wealden rivers, then this becomes stiU more signi- 

 ficant, and the impossibility of the Weald having been under sub- 

 aerial conditions during the prevalence of those excessively detrital 

 agencies that we attribute to ice seems to me obvious — and the more 

 especially when we remember the greater extent which the Lower 

 Greensand formation must have occupied in the earlier stages of the 

 Wealden denudation, all of which, with its great beds of stone in 

 fragments, has gone somewhere. 



Further, the Boulder-clay of the Essex heights is mainly com- 

 posed of rolled chalk ; but it is not the soft chalk of Kent and Surrey, 

 but the hard chalk of Yorkshire and Lincolnshire, termed " Rock " 

 by the well-borers of those counties. The flank of the Lincolnshire 

 chalk-wold for a long distance is occupied by a vast deposit of 

 glacially degraded chalk, so pure as to be extensively quarried for 

 lime, and so thick that the range of country formed out of it rivals 

 in height the Wold itself. We thus see to what sort of detrital 

 accumulation a range of chalk hills has given rise under the powerful 

 action of glacier ice ; and it appears to me but reasonable to expect 

 something of the kind to have occurred over the south-east of Eng- 



