38 Reports and Proceedings. 



Geological Societt of London. — I. November 22, 1865. — W. J- 

 Hamilton, Esq., President, in the chair. The following communica- 

 tions were read : — 1. " On impressions of Selenite in the Woolwich 

 Beds and London Clay." By P. Martin Duncan, M.B,, Sec, G. S. 



Spaces formerly occupied by Crystals of Selenite having been 

 described by the author as occurring in Woolwich Beds near Mot- 

 tingham, Kent, and in the unfossiliferous London Clay of Tendring 

 Hundred, he endeavoured to account for the phenomena to which he 

 had drawn attention. Tlie various facts bearing on the question, 

 including the conditions under which the beds were deposited, their 

 chemical composition, and the mineral condition of the fossils, 

 having been described in detail, Dr, Duncan proceeded to discuss, 

 the explanations that could be suggested to account for the forma- 

 tion and subse(juent disappearance of the crystals. He came to the 

 conclusion that the mineral had resulted from the action of sulphuric- 

 acid, contained in percolating water, on pre-existing carbonate of 

 lime, the s^ulphuric acid having been formed by the oxidation of 

 sulphuretted hydrogen by the oxygen evolved from the decompos- 

 ing vegetable remains occurring in the Plant-beds intercalated in 

 the strata containing Seienite-spaces. Tlie hydrocarbons resulting 

 from the same decomposition would in solution be suiEcient to pro- 

 duce the decomposition of the Selenite, In conclusion Dr. Duncart 

 urged that if his explanations were accepted, the occurrence of 

 Selenite in a deposit must be held to prove the former existence of 

 organisms in it, and the removal of the Selenite to be equivalent to 

 the loss of the evidence of such existence ; therefore there can be 

 no reason why the purest clay-slate may not have been once as 

 fossiliferous as the Woolwich Beds. 



2. " On the Eelation of the Chillesford Beds to the Norwich 

 Crag." By the Eev, 0. Fisher, M,A„ F.G.S. 



The geological position of the Chillesford Clay has never been 

 definitely settled. Mr, Prestwich, who first described it, left the 

 question open as to its identity with the Norwich Crag, or with the 

 more recent marine, freshwater, and land series which immediately 

 underlies the great northern Clay-drift of Norfolk. Sir C. Lyell 

 supports the former view, while Mr. S. Y. Wood, jun., considers 

 the Chillesford Clay a local member of his " Middle Drift." The 

 author described the Chillesford Beds as they occur at Chillesford, 

 and thence traced them northward to Aldborough. At Thorpe, north 

 of Aldborough, the Norwich Crag is exposed, and the main object of 

 the paper was to show that this bed probably overlies the Chillesford 

 Clay. In order to prove that this Crag is not identical with the Mya- 

 bed below the Clay, Mr. Fisher cited its greater thickness, its diifer- 

 ence in lithological character, and the dissimilarity of their fossils ; 

 he also remarked that it rested upon a loamy clay, and contained a 

 strong spring at its base, whereas the Mya-bed was always observed 

 to rest on porous beds ; he therefore inferred that this loamy clay 



