14 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. [NoV. 9, 



subsequently to the accumulation of the Thames gravel, and that 

 their eiFeet was to put an end to that gravel and the coeval gravels 

 of East Essex and of the Canterbury heights, and gradually to raise 

 the sea-bed over Tvent and Sussex, and away to the north of Prance, 

 giving rise thereby to a great submarine denudation — that by this 

 action the inlets in which the Thames and coeval gravels had accu- 



avoided reference to any earlier stages of the Wealden denudation. Mr. Prest- 

 wich, in his ' Memoirs on the Lower London Tertiaries,' gave reasons for sup- 

 posing that the first elevatory action over the Wealden dome preceded the Lower 

 Tertiaries. Those also who agree with him as to the age of the Lenham and 

 Paddlesworth beds, must admit that a considerable planing ofi" of the chalk, 

 exposing probably the subcretaceous strata, was renewed prior to those Lenham 

 and Paddlesworth beds being deposited. I would again call attention to the 

 physical fact, plain to any who will take the trouble to extract the contours from 

 the ordnance map, that there are two distinct sets of disturbances traceable in 

 the south-east of England : — one, the sharp rectilinear east and west upthrows, 

 by which the denudation of the Weald vaJleij has been induced, and which I 

 consider to have affected the Thames gravel, both east and west of London, and 

 to be connected with the similar upthrows of the Isles of Wight and Purbeck (all, 

 therefore, of a date posterior to the first accumulation of the Thames gravel) ; 

 and the other, a set of anterior origin, consisting of a series of concentric curves, 

 the exterior of which is formed by the Cotteswold escarpment, and the next to 

 that by the chalk escarpment from Pangbom-ne to Eoyston, while the inner ones 

 constitute a series of smaller escarpments, of which the trumpet-mouthed gorges 

 in the North Downs, referred to in the paper as river-mouths, successively form 

 parts, the whole set centring near Canterbury. These curves are connected 

 very distinctly with another, and apparently contemporaneous, set, which centre 

 near the western extremity of the Isle of Wight, and are concentric half circles 

 formed by the Lower-Tertiary outcrop of Hampshire and the chalk escarpments 

 of the south-west. The rectilinear movements to which the denudation of the 

 Weald valley is due, have destroyed this anterior curvilinear contour, which is 

 j)erfect up to the points where these rectilinec.r upcasts occur. I formerly sup- 

 posed that these curved groups were, equally with the rectilinear ones, of post- 

 glacial origin ; but an examination of the glacial beds of Bedfordshire and of 

 Northamptonshire showed these beds in such a position relatively to the chalk 

 and oolite escarpments (which form successive concentric curves of the Can- 

 terbury group) as necessitated the inference that the curves were of preglacial 

 origin. These curvilinear movements appear, however, to be clearly synchro- 

 nous with the first denudation of the Tertiaries from the south of England, and 

 with that planing off of the chalk over the Weald, to which allusion has been 

 made. The two jjrincipal rectilinear flexures, by which the direction of the 

 denudation of the Weald valley has been induced, are those of Portsdown Hill 

 and the Guildford Hog's-back ridge, running east and west and parallel to each 

 other, and indicated by lines in Map No. II. The upthrow of these I consider 

 to have so acted on the sea expelled from the north of Kent by the synchronous 

 upcast of the country from there over to France, as to have caused it to denude 

 their regular parallelogrammatic trough formed by the chalk escarpments of 

 the Weald. The two inner curves of the concentric series which centres at 

 Canterbury are visible on the accompanying map. No. I., the innermost of 

 the two being formed by the escarpment which skirts the Canterbury-heights 

 gravel on the west, and extends down to the Weald escarpment above Smeeth. 

 The northern extremity of this ciu've has now disappeared into the north sea. 

 The other, and next outward curve, is formed by the escarpment wliich skirts 

 the East-Essex gravel on the west, and extends down to the Weald trumpet- 

 mouth above Maidstone. The two trumpet-mouths west of this are successively 

 partial repetitions of these curves ; but the next, complete repetition is made 

 l3y the chalk escarpment from Pangbourne to Eoyston ; and the next to this, 

 and last, is the Cotteswold escarpment, prolonged by the oolitic escarpment 

 through Warwickshire, and by the oolitic escarpment of Northamptonshire. 



