Wealden District and the Bas Boulonnais. 3 



to examine also the Bas Boulonnais, for the purpose of ascertaining whether its 

 structure bears any definite relation to that of the Weald. The first part of the 

 communication which I have now to make to the Society contains the results of 

 these investigations ; the second part will contain a discussion of theoretical notions, 

 founded on a general view of the phoenomena of the Wealden districts, together 

 with those of the adjoining country as described by other observers. 



In stating what has hitherto been done with respect to the geological structure 

 of this district, I may notice a section made by the late Mr. Farey from the 

 North to the South Downs, across the centre of the Weald. In the lines of eleva- 

 tion which it recognizes, this section accords with ray own observations ; but many 

 of its details are evidently so entirely hypothetical, that I should not venture to 

 appeal to it on any of the minuter points of structure which it professes to exhibit. 

 It is also impossible, in noticing the labours of previous observers, to omit those of 

 Dr. Mantell, whose name has long been so closely associated with the geology of 

 the south-east of England. If I have been able to make but little use of his obser- 

 vations, it is that our objects have been entirely different ; so that his work, 

 abounding as it does with interesting matter in the department of the science to 

 which it is especially devoted, contains but few observations bearing immediately 

 on the objects of my own researches. 



§ I. The Wealden District. 



It would be useless to enter here into any detailed description of a tract of country 

 of which the general geological features are so well known as those of the district 

 comprised within the bounds of the Wealden denudation. It will only be necessary 

 to state, that the tract to which my researches have been principally confined is 

 bounded on the English side of the Channel by the clearly-defined escarpment of 

 the chalk, extending from the coast near Folkstone, in a north-westerly direction, 

 by the north-east of Ashford and of Maidstone and north of Seven Oaks, and 

 thence in a westerly direction by Reigate, Dorking, Guildford and Farnham, after 

 wdiich it passes to the east of Alton and round Petersfield, whence it proceeds in a 

 nearly easterly, and finally, in a nearly south-easterly direction by Lewes, to the 

 coast at Beachy Head. The Bas Boulonnais is bounded by an exactly similar 

 escarpment of chalk, commencing on the north at Wissant, proceeding by Desvres 

 and Samer, till it again meets the coast seven or eight miles south of Boulogne ; 

 its extent from north to south, parallel with the coast, being about twenty, and that 

 from east to west, along the road from Boulogne to St. Omer, about twelve miles. 

 It requires but little effort of the imagination to connect the two extremities of 



B 2 



