A HISTORY OF SURREY 



and hollows, which remained ever afterwards as the dominant factors in 

 its structure. The dome of the Weald and the trough of the London 

 Basin, referred to in the foregoing pages, are the results of this earth- 

 movement with which we are principally concerned in Surrey. 



In the Wealden dome the strata were raised up in a huge oval 

 tract extending from Hampshire on the west to the Bas Boulonnais in 

 France on the east, now broken through towards the eastern end by the 

 Straits of Dover. ' We must not however overlook the fact pointed 

 out by W. Topley, that the Secondary rocks attained their maximum 

 thickness within this dome, and therefore that its elevation may be 

 in part the result of original irregularities of deposition. 1 But it seems 

 highly probable, though the point seems to have escaped notice, that 

 where the strata are thickest, there also will they be most likely to bulge 

 upwards under lateral pressure, thus accentuating the original inequality. 

 At any rate, there can be no doubt that considerable disturbance tending 

 to elevation has taken place throughout the dome. 



Broadly speaking the Wealden uplift forms a single anticline ; but 

 when examined more closely we find that it is made up of numerous 

 subsidiary waves or flexures, arranged en echelon, which usually rise up 

 gradually from the south and plunge over more steeply towards the north, 

 and flatten and fade out longitudinally. One of these flexures or minor 

 folds explains the sudden expansion of the Lower Greensand outcrop west 

 of Dorking, and its crest brings up a small ' inlier ' of Atherfield Clay 

 and Weald Clay, surrounded by the overlying formations, in the neighbour- 

 hood of Pease Marsh two miles south of Guildford, whilst its northerly 

 plunge gives rise to the steep dips and narrow outcrops of the Hog's 

 Back and its vicinity. Less pronounced waves of the same kind occur 

 farther south between Godalming and Haslemere, and to the eastward 

 near Dorking, Reigate and Westerham. 



But besides these flexures, the strata are sometimes broken through 

 by fractures or ' faults,' between the two sides of which there has been 

 differential movement, so that a once continuous bed now occurs at 

 different levels on the opposite sides of the dislocation. A pronounced 

 ' fault ' of this kind is found about a mile to the eastward of Farnham, 

 where the strata on the north-east side of the fracture are carried down 

 from i 50 to 200 feet lower than the corresponding strata on the south- 

 west side. This fault is sufficiently large to affect the line of outcrop 

 considerably, the Hog's Back ridge being brought to a termination by the 

 setting back of the Chalk escarpment on the west ; and a depression 

 of the surface has been subsequently developed at this point, through 

 which the railway between Farnham and Guildford is carried. Another 

 fault has been traced running east and west from the southern outskirts 

 of Dorking to beyond Wotton, with a downthrow to the north amount- 

 ing in places to 100 feet ; and again at Betchworth, two miles east of 

 Dorking, there is a line of fracture striking from south-east to north-west, 



1 See Quart. Journ. Geol. Sac., vol. xxx. p. 186, and Geology of the Weald, pp. 241, 242. 

 The result of recent deep borings in Kent has added fresh weight to Mr. Topley's argument. 



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