Wealden District and the Bas Boulonnais. 43 



accurate parallelism with each other, according to theory, have been distinctly 

 pointed out, as well as the manner in which the transverse lines are related to the 

 longitudinal ones, and their consequent deviation also from accurate parallelism. 

 The exact accordance of these deviations with those which I have established by 

 observation in the Wealden district constitutes the most complete proof which a 

 theory of elevation can admit of in its application to any district in which we can 

 observe little more than the lines of elevation, and have no means of examining 

 those more minute details of geological structure which the operations of the miner 

 alone can lay open to us. 



9. One conclusion from this theory is, that the whole tract previously defined as 

 extending from the Bas Boulonnais to the south-western part of England was raised 

 by a force acting contemporaneously at every point of the lower surface of the 

 elevated mass, for that hypothesis has been proved sufficient to account for the 

 observed phsenomena. Moreover, it is necessary ; for if this were not the case, con- 

 ceive this area divided into separate portions, each of which was elevated sepa- 

 rately. Then, since it has been shown that the form of the area simultaneously 

 elevated is one of the most essential circumstances on which the directions of dis- 

 location depend, it is manifest that those directions would follow different laws in 

 the different portions successively elevated, which is contrary to the observed phae- 

 nomena. 



10. There is another point of interest on which our theory does not enable us to 

 arrive at an equally demonstrative conclusion : I allude to the question respecting 

 the manner in which the district may have attained its actual geological elevation ; 

 whether by one great upheaval, or by many successive minor ones. The only 

 demonstrative inference to which our theory leads us is this, — that there must have 

 been one considerable decisive and simultaneous movement by which the disloca- 

 tions of the elevated mass were produced ; and I should further regard it as highly 

 probable that this movement was sufficient to impress upon the district its most 

 distinctive and characteristic features, as far as they depend on its geological eleva- 

 tion. I shall not here, however, enter into a discussion of the mere probabilities 

 of the question, for which, in fact, a theory of the denudation of the district is 

 scarcely less essential than that of its elevation. I will only observe, that while we 

 are compelled, as I conceive, to recognise the decisive movement above described, 

 considerations connected with the denudation of the district equally constrain us to 

 recognise in it the slow process of continental elevation. 



11. Our theory also leads us to the inference, that extensive cavities formerly 

 existed within the solid portion of the earth's crust, and, if not always, were at 

 least sometimes filled with fluid or gaseous matter, to the expansion of which the 

 elevation and fracture of the superincumbent solid crust is to be attributed. Eleva- 



g2 



