136 Dr. FiTTON on the Strata below the Chalk. 



heights above Stone Street on the south of Ightham Common. This, if not 

 very much exaggerated, is probably a derangement like those just mentioned. 

 The greater ridge of the Hog's-back itself, on the west of Guildford in 

 Surrey, of which the direction is nearly continuous with that of the ridge at 

 Brasted, may be also connected with it; since the line of the Hog's-back, 

 if prolonged eastward, would pass through the high range of sand hills 

 between Shalford and Martha's Chapel, and thence almost directly through 

 Park Hill, Cockham Hill, and Tilburstow Hill, which last-mentioned place 

 is the seat of a similar disturbance. The distance from Tilburstow to 

 the inclined strata at Moorhouse, is not much more than four miles, and 

 the whole course of this elevated line is almost uniformly from east to 

 west; the line from Moorhouse to Montreal, through Sundridge, deviating 

 from that direction only a few degrees to the north. Mr. Martin has 

 described similar cases of much greater prominence and interest in Western 

 Sussex*. 



(44.) The abrupt rise of the beds in many of these ridges, and the speedy 

 return of the ground to its general inclination, imply the action of a force 

 which, if direct, must have been very near the surface, and too much circum- 

 scribed to be reconcilable either with the effect of gaseous expansion or the 

 impulse of mineral matter in a state of fluidity. The space between the north 

 and south chalk downs seems, in fact, to have been elevated, not by the mere 

 protrusion of one central ridge, but to have been broken up in several different 

 places, so that large portions were thrust outwards, or bent into ridges, by a 

 lateral push, as when a cloth is wrinkled on a table ; a mode of accounting 

 for the formation of such inequalities of the surface, which seems more 

 probable than the action of any direct violence from beneath f. 



* " Memoir, &c.," p. 76 et seq. 



t There is indeed another hypotliesis, which would account for the formation of promi- 

 nences of small extent, by forces originating at very great depths. If we suppose a series of 

 strata, comparatively soft and flexible, to be deposited over a tract composed of older rocks, with 

 hills and ridges on its surface, and the wliole to be then thrust outwards by a force beneath, 

 the protuberances of the lower mass would compress and bend the strata above them into forms 

 corresponding with their own ; —just as in bound books the little inequalities of the cover, or 

 any of the leaves, are impressed on the adjacent pages, and sometimes propagated through a large 

 part of the volume. Nor is this case wholly imaginary. The masses of granite which are found, in 

 many instances, to project above the disturbed strata adjacent to them, must have been elevated 

 after they had cooled, — when their comparative solidity must have been very great : — and among the 

 newer formations, the interval of time between the deposition of many of the groups, now in im- 

 mediate contact, (as of the red marl and the oolites, near Bath, — the mountain limestone and green- 

 sands in the Lower Boulonnois,) must have been more than sufficient both for the condensation 

 of the lower strata, and their subsequent erosion into prominences and valleys, even if the original 

 surface had been uniform. 



