Wealden District and the Bas Boulonnais. 17 



At Piecomb and south-east of Lewes, (the points at which the Greenhurst and 

 Lewes Hues of elevation respectively strike into the projecting chalk mass,) there 

 are two large coombe-like valleys which are worthy of remark, as indicating in the 

 most unequivocal manner, the influence of a line of dislocation in aiding and guiding 

 the operation of denuding causes. Had the action of these causes continued, it 

 is easy to see how, as far as the dislocations may proceed, the projecting chalk 

 between Lewes and Piecomb would have gradually disappeared as much by the 

 process thus indicated on its flanks as by the effect produced on the general front 

 escarpment. From Piecomb to a point directly south of Petworth, as well as to 

 the east of the insulated chalk hill at Lewes, this operation has been completed, 

 which has probably been owing to the more decided character of the dislocation 

 along those portions of the anticlinal lines than between Lewes and Piecomb. I 

 have stated my reasons for doubting the actual prolongation of the Greenhurst line 

 west of the projecting chalk escarpment directly south of Petworth. This projec- 

 tion is probably due to the feebler influence of the dislocation as it approached that 

 point. The two coombe-like valleys above mentioned may afford a useful analogy 

 in forming our conclusions in some other cases to be hereafter described. 



Transverse Valleys near the Greenhurst Line. — On the north-west of Pulborough 

 the river Arun makes its way through the lofty escarpment of the greensand, as 

 described some years ago by Mr. Martin, who also pointed out to me a remarkable 

 and anomalous dislocation at the point immediately east of the transverse valley 

 where the river first penetrates the escarpment. The beds dip north-west at an 

 angle of about 30°, whereas in the vicinity there is a very regular dip to the south. 

 This has been justly attributed 1 think by Mr. Martin to the transverse fracture in 

 which we conceive the valley to have originated. The evidence is precisely similar 

 to that already adduced with respect to the transverse breaks in the Bidborough 

 range. It will be remarked too, that at Lodsworth, west of Petworth, one of the 

 tributary streams to the Arun penetrates the greensand escarpment, in the manner 

 above described. A small stream also descends down a deep valley east of Petworth 

 from the upper part of the greensand range, and Mr. Martin informed m.e that there 

 exists evidence of this valley having in like manner originated in a cross fracture. 



I would also here direct attention to the manner in which the chalk ridge is 

 traversed by the Arun, the Adur, the Ouse and the Cuckmare, circumstances to 

 which I shall again allude in the sequel. 



I shall now proceed to the north-western part of the district. 



The Farnham, Guildford, Dorking and Godstone Line of Flexure. — The most re- 

 markable part of this line is the chalk hill called the Hog's Back, extending from 

 Guildford to a point within about two miles of Farnham, where it ceases somewhat 

 abruptly. The dip at Guildford is considerable, but increases as we proceed westerly 



VOL. VII. SECOND SERIES. D 



