196 Mr. Webster on the Strata lying over the Chalk. 



Other beds of sand succeed, and on the top there is a stratum of 

 dark blue clay a few feet thick. 



This bed, which is frequently referred to by Woodward in his 

 history of fossils, has also excited the particular attention of Mr. 

 Parkinson : but its fossils differ so much from those usually found 

 in the London clay, that it is not easy to decide upon the place to 

 which it ought to be referred ; particularly since it is not even covered 

 by a bed that can be identified with the London clay. Bivalves, re- 

 sembling those of Woolwich, have been brought up in digging wells 

 at other places on the banks of the Thames, but I am not aware that 

 cerithia and the other fossils of this stratum have been so found. 

 This bed is known to extend for a considerable distance on the south 

 of the Thames, in the counties of Kent and Surrey. It is found at 

 Bexley and Plumstead, at which latter place a thin stratum of mi- 

 nute fossil shells was laid open a few years ago, but which no\v 

 appears to be lost. 



At Bromley, which is not far above the chalk, vast quantities of 

 oysters are found imbedded in a calcareous cement and forming, to- 

 gether with rounded pebbles, a sort of rock. It has been observed 

 that these oysters are found adhering to the pebbles, indicating the 

 formation of the latter previous to the growth of the former. 



Woodward, in his catalogue, frequently mentions a bed of stone 

 as occurring at Stilford in Essex, and containing fossil shells w^hich 

 agree with those at Woolwich and Bexley. In a late visit which I 

 made to that part of the country for the purpose of ascertaining this 

 fact, I was not fortunate enough to procure specimens of the rock. 

 It is not indeed now to be seen where it is described by that author, 

 being probably concealed by cultivated ground : but I learned that a 

 stone did exist under the soil, which the labourers frequently came 

 to in ditching, and I mention this in the hope that some one residing 

 in that neighbourhood may ejiamine into this matter. 



