104 Geological Society. 



the natural joints of the schist. The slate immediately in contuct with 

 the trap is, in some parts, quite flinty, having lost its fissile properties, 

 and the colour is changed from purple to black ; but at the distance 

 of two or three feet the slate recovers its natural colour and cleavage. 



A notice of a successful attempt at boring for water at Mortlake in 

 Surrev, by William Richardson, Esq., F.G.S., was next read, an abs- 

 tract of which appears in No. 48 of the Society's Proceedings. 



A paper " On the Strata usually termed Plastic Clay," by John 

 Morris, Esq., and communicated by the President, was then read. 



The author commences by objecting to an arrangement of tertiary 

 formations in different countries according to the classification of the 

 Paris basin bv MM. Cuvier and Brongniart. He then refers to the 

 memoirs of Mr. Webster, Dr. Buckland, and Mr. Richardson, on the 

 strata immediately above the chalk in England, and proceeds to show 

 that they ought to be considered as belonging to the London clay. 



For the sake of convenience in arranging their organic remains, 

 Mr. Morris makes three divisions of these beds : 1. those containing 

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

 Bognor or lower arenaceous beds of the 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 I 



ash coloured sand 



chalk 



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

 Buckland^]", 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 j the former being characterized by the prevalence of 

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



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



\ Geol. Proceedings, vol. ii. p. 72, or Lond. and Edinb. Phil. Mag. vol. v. 

 p. 212. § Geol. Trans., First Series, vol. ii. pp. 196—221. 



f Ibid. vol. iv. p.284. ** Ibid. vol. ii. p. 196. 



