1870.] WOOD WEALD -VALIET DENUDATION. 9 



a map of the drainage-areas and of the elevations will show that the 

 proportions borne by the Chalk, Lower-Greensand, and Hastings- 

 Sand superficies would then remain pretty nearly the same as now — 

 the chief sufferer by such extension being the Weald Clay, owing to 

 the steep upthrow possessed by the Hastings-Sand formation. 



The question then naturally arises, how did any fragments having 

 their parentage within the Weald get into these gravels unless there 

 was an outflow from the Weald ? The explanation oifering itself is that 

 the tidal flow up the inlets in which I regard these gravels as having 

 been deposited would bring such material in moderate quantities from 

 any exposures of the parent rock within the Weald ; and I may ob- 

 serve here how little effect geologists seem disposed to attribute, 

 whether in the way of transport or of denudation, to this powerful 

 and uniform force — the tide. It seems to me that the character and 

 contents of the main mass of the gravels of the Thames, East Essex, 

 and Canterbury heights, composed as they are almost wholly of flint 

 in all stages of wear, from the subangular fragment down to the 

 spherical Lower Tertiary pebble*, is far more consistent with a de- 

 rivation from the wear of a long coast-line of Lower Tertiaries and 

 Chalk than with a derivation from rivers draining, as those of the 

 Weald do, extensive areas of subcretaceous strata abounding in stony 

 beds. 



I now propose to consider the case of the detrital beds within the 

 portion of the Weald here under consideration. 



As before mentioned. Sir Roderick Murchison has shown the great 

 extent and quantity of angular chalk flint which is scattered over 

 the Lower Greensand of the western extremity of the Weald, and that 

 flint and Lower-Greensand debris, with some Tertiary pebble, is 

 scattered over the Weald-clay zone drained by the Eden. In the 

 north-eastern part of the Weald, although angular flints are abundant, 

 the gravels which I regard as anterior to those resulting from the 

 present rivers are more or less mixed with pebbles derived from the 

 Lower Tertiaries. 



The especially noteworthy feature connected with this intermix- 

 ture, however, is that the pebbles and the angular flint present no 

 intermediate grades of rolling to connect them ; so that it is obvious 

 this admixture of angular flint and tertiary pebble cannot, in finding 

 its way to the positions it occupies, have undergone any considerable 

 or repeated amount of wear by transport t. This feature seems to 

 me repugnant to any presumption that these pebbles have settled 



* In this respect the Lower or Fluviatile gravels of the Thames sheet differ 

 greatly from those of the main mass, as their flints are far coarser and more 

 angular, and present less gradation towards the Tertiary pebbles mixed with 

 them. 



t Instances occur, moreover, in which chalk fragments have occurred in this 

 intermixture. Considering how impossible it is for chalk to sustain without 

 dissolution any long-continued aqueous action, this circumstance is also of much 

 importance. The difficulty is enhanced in the case of one of the gravel patches 

 shown in the map as resting on Weald clay west of Yalding, in which Messrs. 

 Foster and Topley speak of chalk nodules having occurred. Their transport 

 there, however, by drainage, in the reversed condition shown in the map, seems 

 to me simple enough. 



