Wealden District and the Bas Boulonnais. 41 



then, as applied to the Wealden district, we have only to compare our theoretical 

 diagram (15) with the map on which the observed lines of elevation are delineated. 

 In doing this, we may, in the first place, direct attention to the central system 

 of observed longitudinal lines. We have not one line, but many, all of which have 

 the same curvature as the geometrical axis of the district ; and we may remark 

 that the three lines of the Bas Boulonnais have exactly the directions they ought 

 to have, if considered as the prolongation of the central system across the Channel. 

 All this is in accurate accordance with our theoretical diagram. Nor is the Green- 

 hurst line less curiously accordant with the line ef (fig. 15)*. The line by Seven 

 Oaks and Farnham agrees with the theoretical line c d and the line g h also 

 becomes almost the exact representative of the well-known line of the Isle of Pur- 

 beck and the Isle of Wight. The central transverse system of fractures follows 

 the theoretical law, as do the fractures also of the chalk escarpment, assuming its 

 transverse river-courses to have originated in such fractures, and the directions of 

 dislocation to coincide with the direction in which the actual rivers penetrate the 

 chalk. It will be observed that the courses of the Wey and the Mole through the 

 northern escarpment are very nearly north and south, while those of the Darent, 

 the Medway and the Stour incline successively more to the north-east as the 

 general axis of the district, and the central longitudinal lines incline to the south- 

 east. This is exactly in accordance with our theoretical deductions ; and though 

 we have no right to cite this harmony as one of the proofs of the theory, in the 

 same manner as if the origin of each river-course in a dislocation had been 

 established by more positive evidence, we may insist upon it as affording strong 

 corroboration of this view of their origin, and of the theory by which we are 

 accounting for it. 



The only sensible deviations from the directions which our calculations assign 

 to the lines of elevation are found in a few of the transverse fractures, more 

 especially in the Seven Oaks ridge, which appear to bear somewhat more to the 

 north-east than the corresponding lines in the theoretical diagram (15). These latter 

 lines, it will be recollected, are determined on the supposition that the structure 

 of the elevated mass has been such as to exercise no sensible influence on the 

 directions of the lines of elevation. It is not, however, contended that the hypo- 

 thesis is necessarily true. The extent to which it must be received in any parti- 

 cular district, is to be determined by the degree of accordance between the observed 

 and calculated results. The almost perfect accordance in the case before us affords 

 the most conclusive proof that can be offered, of the general truth of the supposi- 



* It is easily seen from our observations, at the close of the last article, that this accordance may be 

 regarded as equally perfect, whether the Greenhurst line be one continuous line towards Petersfield, or 

 be formed of two lines, as represented in the map. (See Greenhurst line, p. 15.) 



VOL. VII. — SECOND SERIES. G 



