Wood— On the East Essex Gravels. 399 



The relation tlius borne by the East Essex gravel to the adjacent 

 Lower Tertiaries is preserved all along its termination, although from 

 the original form of the trough the London clay thins towards the 

 Medway. Another line, however, drawn half a mile further east 

 than that of Sect. 14, would give the cutting down still more 

 abruptly.^ Unless the Section so given can be shown to be erro- 

 neous, how (irrespective of the other and concurrent evidence derived 

 from the grouping of the gravels within and without the Weald 

 Valley,) can the conclusion, that the denudation which exposed the 

 Chalk through which the Weald Valley is cut was posterior to the 

 East Essex gravel, be escaped? The Section (14) has been pro- 

 longed into the actual valley of the Weald, in order to show the 

 distinct terracing down of the East Essex gravel, (a; 4^,) to the series 

 x6 that here rests in the Chalk, and from that to the series x<o that 

 occupies the Lower G-reensand terrace ; the distinction in this case 

 from ordinary terracing being, that the great elevatory action which 

 was contemporaneous with the denudation, has elevated the more 

 recent terraces, and depressed the older. To make the terracing 

 appear to descend, the junction lines of the Chalk, Gault, and Lower 

 Greensand should be produced (with the same inclination that they 

 have in the Section) as far as Hoo Common, and the lowermost of 

 them then treated as the horizon for viewing the Section. 



In order to sho"w the complete separation of the channel of the 

 East Essex gravel from that of the Thames gravel, we will take a 

 series of sections across the country dividing the two channels. 

 (See margin of Map for them.) 



In Section 13 a ridge of very high land, extending through Eay- 

 leigh and Hockley, upon part of which an outlier of the Bagshot 

 sand still remains undenuded, formed a well-defined and lofty 

 boundary and valley slope to the western side of the East Essex 

 gravel ; while in Section 15 (which cuts the same ridge more to the 

 south, but which, for the purpose of testing the possibility of any 

 former connection of the two gravels along the Thames mouth, is 

 carried within a mile of the marshes, and parallel to that mouth) 

 we see that this dividing ridge is equally well marked, and is more- 

 over capped at Hadleigh Common and Great Wood by a denudation 

 gravel (flj2) corresponding to one of those shown in the section of 

 the north side of the original Thames Valley. (Section No. 1, Vol. 

 III., p. 58.) Section 16 (drawn still nearer the point where the two 



^ In tlie mapping, by the Geological Survey, of the only portion of the East Essex 

 gravel that has yet been published by them, that within "two miles of Rochester, the 

 gravel is made to overlap the junction of the Loudon clay with the Woolwich beds at 

 Cockham Wood Reach, whereas, it is really divided from the Woolwich beds there by a 

 considerable thickness of London clay, and all three beds, including the gravel, should 

 sweep round parallel to Cockham Wood Reach, and to the scarp of the Downs. The 

 gravel is also not carried far enough in the Survey sheet to the west, there being 

 several exposures beyond the boundary given to it there. The delineation of the 

 gravel in the Survey sheet is so made as to appear at this part as though the chalk 

 sides of the Weald Valley had been formed before the gravel came into existence. 

 The corrected delineation at this part is given in an enlargement at the foot of the 

 Map accompanying this paper. No distinction is of course made in the Survey Map 

 between this gravel and those which I have grouped as several successive series. 



