451 



the Reading oyster ; 2. the Woolwich and Upnor strata ; and 3. the 

 Bognor or lower arenaceous beds ofthe London clay. 



The first division has been long well known in consequence of the 

 sections given by Mr. Webster * and Dr. Buckland f of the Catsgrove 

 pits near Reading; and has been subsequently described in a paper 

 by Mr. Rofe on the same district J. Mr. Morris gives the following 

 sections of this deposit at Northaw in Hertfordshire, and Headley in 

 Surrey. 



Feet. 



Northaw, Top, grey sand 20 



green sand with oysters 1 



grey sand 2 



iron flint bed 8 inches. 



chalk 



Feet. 



Headley, Top, red and green variegated marls 4 



clay and sand 3 



grey sand with oysters 1 



ash-coloured sand 



chalk 



2. The Woolwich strata, also described by Mr. Webster § and Dr. 

 Buckland^f, extend along the south side of the Thames, and patches of 

 them are said to occur near Stifford** and Plaistow in Essex. They 

 are chiefly composed of sand, clay, pebbles, and calcareous rock, the 

 strata varying greatly in their thickness in different parts of even the 

 same pit ; and in their order of succession in different localities. At 

 Woolwich, Sundridge park, Upnor, and some other places, there is 

 also a marked distinction in the fossils of the upper beds from those 

 of the lower ; the former being characterized by the prevalence of 

 freshwater or estuary shells of the genera Cyrena, Neritina, Melanopsis 

 and Planorbis, associated with marine shells. How far this distinction 

 maybe owing to the action of a river, Mr. Morris says it may be difficult 

 to determine, as the recent species of the above genera have variable 

 habits. The principal localities at which the Woolwich beds have 

 been noticed are, Sundridge park near Bromley, Chiselhurst, Orping- 

 ton, Beckenham, Sydenham, Counter Hill, Loam-pit hill near Lewis- 

 ham, the Thames Tunnel, Vauxhall, the road leading from Oldfield to 

 Plumstead; the ninth milestone beyond Shooter's Hill, Erith ballast- 

 pit, Bexley Heath, Swanscombe Wood, Green Street near Stoke, and 

 Upnor near Rochester. 



The following sections presented at the last locality, illustrate the 

 variations in different parts of the same pit. 



Feet. 



South End, Top, brown clay with fragments of chalk and 



chalk flints 10 



fine calcareous clay 3 



sand with bluish flint pebbles, and numerous re- 



* Geol. Trans., First Series, vol. ii. p. 198. f Ibid. vol. iv. p. 278. 



i Geol. Proceedings, vol. ii. p. 72. 

 § Geol. Trans., First Series, vol. ii. pp. 196 — 221. 

 t Ibid, vol.iv. p.[284. ** Ibid. vol. ii. p. 196. 



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