410 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 24, 



General average thickness. 



Westward Eastward 

 area. area. 



Zones. Feet. Feet. 



Fossiliferous localities. 



T,. ^ , ' ,\ nn icA f Cliffs of Slieppey and of Southend; Brent- 



First (uppermost). 70 150 | wood-hill ; Egham-hiU. 



Second. 80 100 Margaretting-street, near Chelmsford ; High- 



gate Archway*; Wandsworth Common; 

 Railway station, Crystal Palace ; Newn- 

 ham ; Clewet's-green. 



Third. 100 140 Cliffs between Heme Bay and Whitstable; 



Colchester ; Chalk-farm ; Primrose-hill ; 

 Copenhagen-fields; Islington; Whetstone; 

 Hornsey; Colney Hatch; Kew; Brentford; 

 CiiffeU. 



Fourth. 50 90 Harwich; Walton; Cliff east of Heme Bay (?) ; 



Potter's-bar (?) ; Hedgerly ; Old Basing ; 



Sherfield ; upper part of Pebble-hill and of 



300 480 Clarendon-hill; Bognor. 



A question arises, whether the upper beds of the London Clay in 

 Kent and Essex may not represent some portion of the Lower 

 Bagshot or Bracklesham sands of Berkshire and Hampshire, or 

 whether the 200 to 300 feet of London Clay of the latter district 

 represents, in mass as well as in time, the 460 to 480 feet of the 

 former district. I am inclined to take the latter \T.ew, and to 

 consider the eastern district to have derived its superadded features 

 from its proximity to the sources of the river supply of the period, 

 and to the greater depth of the sea in that area (or to a more rapid 

 subsidence of the bed of the sea), so as to allow of a larger accumula- 

 tion of sediment, and to result in a greater depth of strata. 



§ 3. Lists of Organic Remains. 



As no separate and complete lists of the fossils of Sheppey, High- 

 gate, and other localities mentioned in the text have been published, 

 I have endeavoured to determine with some accuracy these different 

 faunas. There are, fortunately, several special collections of great 

 value to assist an inquiry of this nature ; Mr. Wether ell, who has 

 materially assisted me in this inquiry, having for many years zealously 

 collected all the fossils found at Highgate and its vicinity (the road 

 at the Archway on Highgate-hill, the railway cuttings at Primrose- 

 hill, Copenhagen-fields, Hornsey, and Whetstone, &:c.); whilst Mr. 

 Bowerbank, on his side, has amassed a like unrivalled series of the 

 Sheppey fishes, reptiles, Crustacea, and plants. The collection of Mr. 

 Edwards from both these places, although subordinate to his admirable 

 collection of Bracklesham Bay fossils, is very important. More re- 

 cently Mr. Luun has formed a valuable collection of the Southend 

 fossils. My own attention has been chiefly turned to such less im- 

 portant localities and sections, as from their distance ortemporarynature 

 have not come within the examination of such assiduous collectors. 



Further, the valuable publications of the Palseontographical Society 



* The beds at Finchley and at Haverstock-hill would seem to occupy a position 

 intermediate between these second and third zones. The zones may possibly 

 be multipUed. 



