352 'Wood — Structure of Valleys in Essex. 



Drift, occupying the plateau stretcking by Hitchin to Eoyston, and 

 tliat opposite stretching from Shefford by Biggleswade and Caxton to 

 near Cambridge, and the gi-eat trough excavated between the Upper 

 Drift crowning the heights from Eockingham towards Market 

 Harboro' and that croAvning the opposite heights of south-eastern 

 Leicestershire. In none of them, however, is the tumescence so 

 decided as in the ridge shown in the section, which being nearer 

 to the centre of origin (near Canterbury) is proportionately more 

 decisively marked. 



The valley of the Crouch like that of the Blackwater also consists 

 of two distinct portions, the lower and the upper. The lower con- 

 sists of a rectilinear fissure which has passed at right angles through 

 the older trough occupied by the East Essex gravel, and through 

 that gravel itself ; in which respect it is identical with the mouth of 

 the Thames. The upper valley, on tlie other hand, is of similar 

 origin to that of the Blackwater estuary, having been, in fact, 

 before the re-excavation, to which I am about to allude, a part of 

 the same valley. 



For the ]Durpose of showing the nature of these valleys I have 

 carefully delineated on the accompanying Map the principal valley 

 contours. It will be seen that the great rolling ridge intersected by 

 Section 9 is precisely a repetition of the ridge nearer the sea, which, 

 forming one side of the valley that contained the East Essex gravel, 

 and rising far above that gravel, is cut sharply down on its western 

 side towards the Blackwater estuary; and that this latter ridge, 

 after being cut through at right angles by the Crouch valley, com- 

 mences again and proceeds in a continuation of the same curve to 

 Benfleet. It will also be seen that the inland boundary of the East 

 Essex gravel very closely coincides with this ridge, and there will 

 be no difficulty, while keeping these features in the eye, in realizing 

 the idea, which I am desirous to convey, that the original trough lying 

 between these two great ridges (which had been formed, but in a less 

 marked manner, by the denudation that accompanied the emergence 

 of the country from the Boulder-clay sea) , has been re-excavated and 

 deepened as far south, probably, as Pitsea ; and that in this way the 

 original contour has been so shai'ply marked as to present the very 

 decided features which it now possesses. It is apparent from it, too, 

 that the Crouch, in its former more extensive estuarine dimensions 

 — due to the lower level existing at this part at the period of 

 its formation — cut for itself a way through the original ridge 

 that formed the western brow of the valley in which the East 

 Essex gravel was deposited, and appropriating to itself the south- 

 western end of the great trough that lay on the west side of 

 this brow, divided itself from the Blackwater by eroding the 

 ridge which stretches from Althorn to Cold Norton. The Black- 

 water estuary, in its similar former estuarine extension, it will 

 be seen, has done the same thing on the north side of that ridge, 

 and, by the subsequent elevation of the block of land lying between 

 the Blackwater estuary and the mouth of the Thames, the Crouch 

 river and the Blackwater estuary have both retreated to their present 

 dimensions. 



