92 REPORT— 1872. 



described generally as consisting of thick accumulations of sands and sand- 

 stones for a lower or earlier part, surmounted by a great argillaceous deposit 

 (AVeald Clay). Mr. Webster suggested the propriety of uniting the Purbeck beds, 

 Hastings sands, and Weald Clay into one group, the whole being mainly a conse- 

 cutive freshwater series. It must be understood, however, that there is not a 

 definite line separating the Hastings sands from the Weald Clay : all that is signified 

 is, that sands predominate for the lower, and claj's for the upper portion of the 

 Wealden depositions ; but just as thick bands of clay occur in the lower series, so 

 bands of sandstone occur in the upper. 



The arrangement adopted by the Geological Survey, in descending order, is : — 

 Weald Clay,Timbridge- Wells Sands,Wadhurst Clay, Aslidown Sands, Ashburnham 

 beds (which, in Sussex, are the equivalent of the Purbeck beds of Dorsetshire). 



The lower sands are well seen on the coast at Hastings, whence they took their 

 name, and extend thence continuously to near Horsham, rising into the central 

 ridge of the Wealden elevations of St. -Leonards, Tilgate, and Ashdown forests. 

 On every side this tract is bounded by the Weald Clay, which extends to the ha^e 

 of the escarpment of the Lower Green Sand, beneath which it passes. 



This surface of freshwater strata, so defined, extends for seventy miles from 

 E. to W., and has a breadth from N. to S. of thirty-five miles. Over the whole of 

 this area the freshwater depositions attain a great thickness ; the lower sandy group 

 may be taken as 800 feet, and the Weald Clay as 4o0 feet at least. 



To realize the conditions under which these accumulations were formed, the 

 now upraised central sandstone ranges must be put back to their original horizontal 

 position, and the whole series must be regarded as the infilling by freshwater 

 rivers of what was an area of depression with reference to the terrestrial surface 

 of the time. This Wealden formation can be traced far beyond the limits of the 

 denudation of the S.E. counties. In a southerly direction it occurs in the Isle of 

 Wight, with its two divisions of Weald Clay and Lower Sands. In this 

 quarter the Weald Clay is reduced to a thickness of 68 feet. In a westerly 

 direction (Swanage Bay) the Wealden sands have a great thickness, and are 

 surmounted by only a thinnish band of Weald Clay or deep-water deposit; 

 and both divisions decrease rapidly in the extension of the formation across the 

 Isle of Purbeck, and liave not been recognized in the Isle of Portland, from which, 

 if they even extended there, they must have been denuded off. 



In a northerly direction, several sections about Oxford, as from Shotover Hill to 

 Great Hazeley, from AMieatley to Tetsworth, from Brill tlirough Long Crenden to 

 Thame, from Whitchm-ch to Aylesbury, extending from S.W. to N.E. for a breadth 

 of thirty miles, show Purbeck beds and freshwater ferruginous sands passing be- 

 neath Cretaceous beds. It is obvious that the Wealden formation has been cut 

 back in this quarter, and that originally it had a much greater extension. In this 

 quarter, too, the ferruginous sands overlap the Purbeck beds, showing that the lake 

 had here widened its area beyond the dimensions of the Purbeck lake. 



From Oxford* to the Vale of Wardour is an interval of seventy miles, from over 

 which the Portland Oolite has been removed, except at Swindon, at which place 

 there are beds which are unmistakably referable to the Pm-beck group ; and it is 

 a fair inference that it is to this denudation that is to be attributed the absence 

 of the lacustrine depositions which everywhere on our area, and on much of 

 that of continental Europe which was adjacent, follow next upon the Portland 

 stage. Such being the case, the smallest possible dimensions which can be as- 

 signed to the great Wealden lake, are that it extended from bej'ond Aylesbury 

 to Portland for 120 miles, and from Portland to to the Boulonnais "for 200 

 miles. 



From Rye to Portland the Wealden beds pass out of sight beneath the level 

 of the English Channel. The valley of the Channel is the result of the dis- 

 turbance which produced the E. and W. lines of the South of England, and 

 was produced subsequently to the Nummulitic period. 



Dr. Fitton remarks that, the subdivisions of the Wealden formation, especially 

 at its upper part, being in some measure arbitrary, it is difficult to determine to 



* Vide evidence as to range of Wealden deposits, Pliillips's ' Geology of Oxford.' 



