102 



Wood— Structure of the Thames Yalley. 



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I will now endeavour to show more 

 distinctly the destruction of the eastern 

 part of the original valley. Section 6 

 (drawn at right angles to Section 1) shows 

 the Higham fragment and fault. From 

 this it will be seen that the trough of the 

 original valley, before it was broken up, 

 passed by Chad well (near Tilbury), where 

 it was cut down to the Thanet sand ; the 

 sides of it rising again towards Higham, 

 where the gravel fragment, underlaid by 

 London clay, indicates the slope of the 

 valley in that part, before it was destroyed, 

 to have corresponded with that on the 

 opposite side towards Orsett, where the 

 gravel, still remaining in an unbroken 

 sheet, spreads up from the Thanet sand, on 

 which it rests more in the trough, till, at 

 Orsett, it rests on a thickness of London 

 clay. The section does not cut the original 

 valley at right angles, but takes a slice off 

 its edge only, this being unavoidable, in 

 order to catch the most crucial of the evi- 

 dences which have been spared to us, and 

 the centre of the trough is therefore not 

 quite reached in this section ; that centre 

 passing more to the west, hj Grays, where it 

 cuts almost through the Thanet sand, so that, 

 in that neighbourhood, the Thames gravel 

 is divided from the Chalk by a very small 

 thickness of the Lower Tertiary sands. 



It is not, however^ in the eastern part of 

 it alone that we find evidence of the con- 

 nection of the original valley with the sea 

 over the Weald. The Thames gravel, al- 

 though thinned, can be followed in places, 

 without a break, up the gradual slope which 

 forms the north side of the Eichmond and 

 Wimbledon Hill from the great sheet that 

 lies on both sides of the river at the lower 

 level, until it joins the expanse of gravel 

 covering the hill top ; but on the other 

 three sides, as well as on part of the fourth;, 

 the expanse on the hill is detached from 

 the sheet of the low ground by lines of 

 denudation that are in some parts gradual, 

 but in others, as on the west of Eichmond 

 Park, so sharp as to amount to almost a 

 cliff; while, as before observed, the hill 

 has no counterpart on the opposite slope of 



