the Purbeck and Wealden Deposits of England and France. 271 



formation was almost reached ; the delta of the Rhone has been 

 pierced for 400 feet*; but I am not aware that borings have 

 anywhere shown the existence of delta-deposits of even half the 

 thickness of the purely freshwater beds of the Wealden proper, 

 much less of the united formations of the Purbeck and Wealden ; 

 while in almost every case the borer appears to have passed 

 through intercalated beds showing land- surfaces, and through 

 conglomerates, of which the Wealden furnishes no parallel. 



In attempting to realize the peculiar geographical configura- 

 tion of the South-east of England during the Wealden epoeh, it 

 will be well to refer to the grouping of the strata that surround 

 the Wealden deposits. The anticipations of Mr. Godwin- Austen, 

 in his paper "On the possible extension of the Coal-measures 

 beneath the South-east of England "fj were to a certain extent 

 confirmed by the well-borings which took place about the same 

 time in the north of London and at Harwich. In the former, 

 after passing through the tertiaries, chalk with flints, chalk 

 without flints, upper greensand, and gault, to an aggregate 

 depth of 1113 feet, the borer reached a group of beds into 

 which it passed for 188 feet, and which did not appear to belong 

 to the lower greensand, but more probably, in the absence of 

 recognizable fossils, to the trias. In the latter case the borer, 

 after passing through tertiaries, chalk, upper greensand, and 

 gault, reached a black slaty rock which, in his description of 

 the boring, Mr. Prestwich says can, it is almost certain, only be 

 referred to one of the palaeozoic groups. The evidence afforded 

 by the latter of these borings appears sufficient to substantiate 

 the production, beneath the eastern counties of England, of the 

 palaeozoic axis of the Ardennes, which had been traced by borings 

 to extend beneath the chalk as far west as Calais. The direction 

 in which this axis is produced, however, appears to me to be 

 more probably that adopted by Mr. Hull J, viz. in the direction 

 of the Warwickshire and South Staffordshire coal-fields, than 

 in that adopted by Mr. Godwin-Austen, the direction of the coal- 

 measures of the West of England. The borings which have been 

 made through the chalk in the Pas de Calais and Departement 

 du Nord §, show that the coal there, occurring beneath a thickness 

 of from 260 to 600 feet of overlying upper cretaceous deposits, 

 lies in a trough of carboniferous limestone and Devonian rocks 

 which stretches in the form of a slight curve having its convex 

 side towards the S.S.W. The production of this curve extends 



* Principles of Geology, 1850, p. 260. 



f Quart. Journ. Geo! Soe. vol. xii. p. 38. 



X Ibid. vol. xvi. p. 66. 



§ Degoussee and Laurent, Quart. Journ. Geol. Soc. vol. xii. p. 252. 



