294 EOCENE PERIOD. [Ch. XXI. 



lines, which form ridges and troughs running nearly parallel to 

 each other. 



Much of the picturesque character of the scenery of this dis- 

 trict arises from the depth of the narrow valleys and ridges to 

 which the sharp bends and fractures of the strata have given 

 rise ; but it is also in part to be attributed to the excavating 

 power exerted by water, especially on the interstratified argil- 

 laceous beds. 



From the above description it will appear that, in the tract 

 intervening between the North and South Downs, there are a 

 series of parallel valleys and ridges ; the valleys appearing evi- 

 dently to have been formed principally by the removal of softer 

 materials, while the ridges are due to the resistance offered by 

 firmer beds to the destroying action of water. 



Rise and denudation of the strata gradual. Let us then 

 consider how far these phenomena agree with the changes 

 which we should naturally expect to occur during the gradual 

 rise of the secondary strata. Suppose the line of the most 

 violent movements to have coincided with what is now the cen- 

 tral ridge of the Weald Valley; in that case, the first land 

 which emerged must have been situated where the Forest ridge 

 is now placed. Here a number of reefs may have existed, and 

 islands of chalk, which may have been gradually devoured by 

 the ocean in the same manner as Heligoland and other Euro- 

 pean isles have disappeared in modern times, as related in our 

 first volume *. 



Suppose the ridge or dome first elevated to have- been so rent 

 and shattered on its summit as to give more easy access to the 

 waves, until at length the masses represented by the fainter lines 

 in the annexed diagram were removed. Two strips of land might 



No. 69. 



Sea 



then remain on each side of a channel, in the same manner as 

 * Page 289, and Second Edition, page 330. 



