1868.] WOOD PEBBLE-BEDS. 467 



vorume of the Quarterly Journal, rounded pebbles are scattered over 

 this outlier also. We derive no assistance in the reference of these beds 

 to their true geological age from organic remains, as they appear to 

 be entirely destitute of anything of the sort. 



It is important to observe that some of the earliest Postglacial 

 gravels have been chiefly made up of these beds redcposited ; and in 

 such form they are sometimes difficult of distinction from the original 

 bed. These redcposited pebbles may, however, usually be distin- 

 guished by the presence among them of angular flints, derived from 

 the denudation of the Glacial Clay ; but as the two sets of gravels are 

 often in conjunction, without any distinct line of demarcation, care 

 is required not to confound them, almost every mass of these older 

 pebbles being overlain by a few feet of Postglacial pebble-gravel, 

 Avhich, though made up of the redeposit of the older bed beneath it, 

 contains an intermixture of stones derived from various rocks. The 

 pebbles of the beds which I have first described, namely, those in- 

 variably associated with the Bagshot outlier, and numbered 4, have 

 also been redistributed by the Postglacial denudation in the form of 

 feeble gravels, and gravelly warp, over the London Clay and passage- 

 beds — their chief places of occurrence in this form being at Hawk's 

 Hill Wood, Ongar Park Wood, Tawney Wood, and Beachet Wood, 

 all on the east and south-east of Epping in Essex. These feeble 

 gravels and gravelly warp are omitted from the section accompanying 

 this ;paper. 



In addition to this the pebble-beds (No. 4) appear to me to have 

 formed the principal source of the pebbly gravel which, in an inter- 

 mittent way, underlies the Glacial Clay in places where that clay is 

 at high elevations in Essex, Middlesex, and Herts ; this pebbly 

 gravel is that described by Mr. Hughes as the " Gravel of the Higher 

 Plain," and is shown in the accompanying section by the number 6. 

 The distinction of this from the more extensively distributed Middle 

 Glacial gravels, which similarly underlie that clay (but in these 

 counties at lower elevations), I also pointed out in the memoir 

 before referred to. The same desire to compress, however, caused 

 me to omit from the paper on the Postglacial structure of the 

 south-east of England any reference to them, beyond a symbol* in- 

 dicative of their place in the diagram -sections, which were given in 

 that paper (vol. xxiii. p. 396) for the purpose of showing the mode 

 in which the incidence of the Glacial Clay took place over the area 

 now forming the northern heights of the Thames valley. The oc- 

 currence of what I deem the same bed in Herts having, however, 

 formed the subject of the paper of Mr. T. M'K. Hughes, before re- 

 ferred to, I think it desirable to advert here to what I believe, from 

 a study of it in the parts lying beyond that embraced in Mr. Hughes's 

 paper, to be its age and origin, having come to a different conclusion 

 on this point from that gentleman. 



* See bed 6' in figs. 2 & 3, p. 396, of the 23rd vol. of the Quarterly Journal ; 

 unfortunately, by a typographical error, that symbol is omitted in the descriptive 

 reference to those diagrams, and should come in between the words " clay " and 

 " occasional " in the description of bed No. 6 in those diagrams. 



