290 



THE GEOLOGIST. 



f - £ 



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 ; g, Old Wealden land. 



We have already pointed 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 heen 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 upheaving 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 Pig. 12.) 



As certain as the laws of mathematics are the laws of such eleva- 

 tions. The 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. 8. Fig. 9. Fig. 10. ' 



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 j and the consequence of the upheaval of a dis- 



