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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Apr. 21. 



Fig. 7. — Diagram showing the conditions that would have resulted 

 from the deposition of the Cretaceous Beds on the edge of a shoal 

 formed by the previous elevation of the Weald. 



N. S. 



Elevated mass of the Weald. 

 Cretaceous beds. 



1 & 2. Lower Cretaceous strata, thinning out to the south, 

 whilst the Upper strata overlap successively 

 upon the Wealden rocks. 



Fig. 8. — Diagram showing the relative thickness of the Lower Creta- 

 ceous beds, and the denudation of the Chalk, over the Weald. 



N. Shoal or Island S. 



in the Tertiary Sea. 



c. Chalk. 

 d, e. Upper Greensand and Gault. 



/. liower Greensand. 

 g, Wealden. 



[The lower beds of Chalk below x should have been represented as rather thicker and the 

 Lower Greensand rather thinner.] 



of the Upper Greensand period and at the dawn of that of the Chalk ; 

 still it was not of that extent to prevent the extension over the southern 

 area of an important mass of lower chalk and of the middle chalk with 

 flints. Neither the upper nor the lower chalk, however, possess that 

 great development which they do in Herts and Cambridgeshire' — the 

 one apparently having been removed by denudation, and the other 

 originally deposited in a thicker mass. 



On either alternative, of a depression in Cambridgeshire or an ele- 

 vation in Kent, the result would still be the same, in that we should 

 have the chalk surface relatively higher and nearer to the sea-level in 

 the latter than in the former county. This would favour the wear- 

 ing down of the chalk by the action of the sea over the present area 

 of the Weald, and as we see reason to believe that the chalk within 

 that area was removed or reduced to a thin shell, it is probable that 

 some of the underlying beds of the green-sand or even of the Wealden 

 might have become exposed to the denuding action. See fig. 8. 



There is no appearance, however, in the Lower Tertiaries of debris 

 derived from any large mass of clay such as the Wealden, whereas 

 the light-coloured sands, with traces of greensand and occasionally 

 of carbonate of lime, forming the Thanet Sands, have a mineral cha- 

 racter perfectly harmonising with a reconstruction out of the Upper 

 Greensand chiefly, with the Gault and upper part of the Lower Green- 

 sand partially. It would thus seem that only these portions of the 

 lower cretaceous series had, together with the Chalk, at that time been 

 raised to the surface, and furnished materials for the Thanet Sands. 



