290 
TUE GEOLOGIST. 
Fig. 6. — Ideal section of strata thinning out against a ridge. 
a, Upper Chalk ; b, Lower Chalk ; c, Upper Greensand ; d, Gault ; e, Lower 
Greensand ; f, Keocomian beds ; ff, Old Wealdeu land. 
We have already poiDted out the convergence of the lines of dip 
towards a point near Battel. There was the apex of the great dome, 
the outer concentric coatings of which, whatever their original thick- 
ness, have since been sliced off — denuded by cutting action of the 
waves as the island-dome was slowly elevated out of the waters. 
Now the physical features of this region, as we at present see 
them after its upheaval, show that the area uplifted was the area 
of weakest resistance to the uplieaving or expansive forces below, 
and that that area had a configuration not unlike that it still retains, 
although it would appear that the denudation of the upper beds was 
carried on synchronously with the gradual upheaval of the mass 
throughout, at least throughout the early Tertiary period, and since 
the fracture of the river-valleys, at least over the area enclosed by 
the downs, from which the debris of the shattered beds has been 
cleanly removed. (See Fig. 12.) 
As certain as the laws of mathematics are the laws of such eleva- 
tions. Tlie hills, irregular as they appear to be, are not vagaries of 
nature, nor are the valleys fortuitous cavities. The Wealden area 
is an irregular curved oval, cut through by the fissure of the English 
Channel ; the counterpart encompassing the neighbourhood of Calais 
and Boulogne. 
If one applied a pressure from beneath to a deal table, a tile, or 
any other square or straight-sided object, it would split linearly across 
Fig. 7. Fig. 
Fis. 9. 
Fig. 11, 
in one direction or the other, as in Fig. 7 or Fig. 8. If one 
applied the pressure against the under surface of a drum-head, the 
parchment would split either in concentric lines, as in Fig. 9, around, 
or in radiating lines, Fig. 10, from the centre. Now, an oval is prac- 
tically a compound of the square or parallelogram and the circle, 
as shown in Fig. 11 ; and the consequence of the upheaval of a dis- 
