1870,] WOOD WEALD-TALLEY DENUDATION. 7 



land, had that region been under subaerial conditions during the 

 prevalence of this icy envelope ; yet, after alloAving for the excessive 

 denudation which has, as it seems to me, prevailed in postglacial 

 times over the south-east of England, the complete absence of the 

 smallest vestige of any such accumulation as we find in Lincolnshire 

 is, I think, reconcilable only with the conclusion that during the 

 formation of the Boulder-claj'' this region was covered by the sea — 

 a conclusion, moreover, to which the position of the Bouldor-clay at 

 elevations of 300 feet and upwards on the Essex heights that front 

 the North Downs equally points. 



So far, therefore, as the evidence of the detrital beds of Glacial 

 age lying without the north-eastern part of theWeald affords a test, 

 we are, I think, entitled to infer that the Weald was not during the 

 climax of the Glacial period an area undergoing denudation by streams 

 either of water or of ice, and, indeed, that, with the exception of the 

 earlier part of that period, it was not above water at all, , 



Passing now to the Postglacial beds, the principal formations of 

 this age lying without the Weald are the gravels to which I have 

 already made allusion under the names of the gravels of the Thames, 

 of East Essex, and of the Canterbury heights. 



Precisely the same kind of reasoning is applicable to these as to 

 the case of the Glacial beds, so far as concerns the debris of sub- 

 cretaceous rocks. If the Stour, the Med way, and the Daren t, 

 running outwards from the Weald, had effected any thing like the 

 prodigious denudation attributed to them, fragments of the stone- 

 beds of the Lower Greensand ought to make up at least half the 

 volume of the Thames, the East-Essex, and the Canterbury-heights 

 gravels where these three streams pass through them. 



In the Thames gravel of this part, however, such fragments, 

 though common, form but a small proportion of the gravel mass, the 

 bulk of which is flint with some quartzites intermixed. The East- 

 Essex gravel, both where it lies within the valley of the Medway 

 between the Nore and Rochester, and where it extends along the 

 east coast of Essex, presents similar features ; while the gravel of 

 the Canterbury heights, which forms the sides of the valley through 

 which the Stour flows, is even more exclusively flint in its compo- 

 sition, as it requires a search of some time to find half a dozen frag- 

 ments of any other material, so that in this gravel the proportion 

 of any other material than flint is probably not yjj'uu of the mass. 



If we reflect how small is the elevation of these gravels above the 

 streams which flow beneath them, in comparison with the elevations 

 which the subcretaceous rocks attain within the Weald, can it be con- 

 tended that gravels so composed could have been deposited from rivers 

 which were effecting the enormous denudation that has placed these 

 rocks as they now are ? Can we, even if we reject the hypothesis of 

 this great flixviatile denudation, reconcile the composition of these 

 gravels with their deposition from these rivers when in greater volume 

 than now ? 



The answer seems to me to be clearly negative, and that under such 

 circumstances the flint in the East-Essex gravel between Eochcster 



