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 Avhat 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. 
then remain on each side of a channel, in the same manner as 
* Page 289, and Second Edition, page 330. 
