the London and Hampshire Basins. 191 



when speaking of the drift on this side of the Channel. This 

 gentleman ventures also to use the word " debacle/' and speaks 

 constantly of the denudation as a '^ great catastrophe/' With 

 all this evidence before us, it seems then to be no great stretch 

 of the imagination to suppose that all the tertiaries follow the 

 secondary in the same order of denudation. From the nature of 

 their materials^ we do not wonder that they do not present the 

 bold and prominent escarpments of the chalk and greensands ; 

 they lie beveled off in succession, as they crop out within the 

 borders of the so-called chalk-basins. At the back of the Surrey 

 Hills and South Downs we find the plastic clay and sands thinned 

 out on the chalk. More remotely from the chalk hills, succeed 

 the beds of London clay and tertiary limestones ; — at Brackles- 

 ham and Bognor on one side, and in the bed of the Thames and 

 at Sheppy on the other. Where the materials of these tertiaries 

 are of firmer texture and have afforded more resistance, and 

 where their synclinal position has given them protection, we still 

 find some signs of escarpment in them, as, east of Croydon, in 

 the Addington and Keston Hills, and north of Farnham, at Farn- 

 ham Beacon, and in the line of country north of the Hogsback. 

 The only escarpment exhibited by the tertiaries south of the South 

 Downs, and that is synclinal, is the cliff at Castle Hill, described 

 by Dr. Mantell*. From this point westward great ravages have 

 been made; but I can say with confidence that considerable 

 relics of these beds exist in the synclinal of what I have called the 

 chalk "Outlier-by-protusion'' at Highdown Hill near Worthing f; 

 again in the eminences between Arundel and Angmering. Shingle 

 beds of this sera show strongly also at Box-grove. And all the 

 tract of country called the " Manwood,'' between Chichester and 

 Bracklesham, is plastic clay, with an occasional sprinkling of 

 diluvium. West of Chichester, and north of Emsworth again, 

 the plastic clay emerges from beneath the thick beds of drift 

 that abound in this line of country. And the forest of Bere, 

 which is the synclinal of Portsdown, is wholly tertiary. With this 

 comprehensive view before us of the general denudation of all 

 the beds on and about the great line of elevation, and looking on it 

 as the last great change that has come over the S.E. of England^ 

 we discard all notions of marine deposit of a more recent date, 

 or in other words, as asserted in my memoir of 1828 before 

 alluded to, '^the chalk basins so often spoken of, never could 

 have been areas of deposit for beds not to be found also on the 

 denuded surfaces, at the same level." 



2. We pass now to the consideration of the second order of 

 phsenomena, — the valleys and lines of drainage. Although it is 



* Mantell's Geology of S.E. of England, p. 55. 

 t Geol. Mem. of Western Sussex, pp. 95, 96. 



