Mr. Webster on the Strata lying over the Chalk. 197 



It is said that thin strata of a calcareous rock are found in sinking 

 wells through the London clay ; but of this I have not seen any- 

 well authenticated specimens. The circumstance however is far from 

 being improbable. 



The extensive works now carrying on in the neighbourhood of 

 the metropolis, as the cutting the hill at Highgate, the tunnel 

 lately carried under the Thames at Rotherhithe, one under Hyde 

 Park, the canal now forming in the Regent's Park, and several 

 others of a similar kind, have thrown great light upon the nature 

 of the London clay and its fossils, and furnish daily opportunities 

 for observation highly useful to all those who are interested in the 

 examination of our upper strata. 



At Highgate-hill the beds consist of 



1. Vegetable mould. 



2. Several feet of loose gravel and highly ferruginous masses of sandstone. 



3. Yellow clay. 



4. Blue clay, in which great numbers of marine shells and parts of fish 



were found. 



On the south side of the River Thames near Rotherhithe, a shaft 

 sunk for a tunnel proposed to be carried under the Thames, exhibited 



the following strata. 

 Feet 



6 9 Vegetable mould. 

 9 Brown clay. 



20 8 Gravel with water. 



3 Blue clay. 



b 1 Loam. 



3 9 Blue clay with bivalve shells. 



7 6 Gravel stones imbedded in a calcareous rock. 



4 6 Light blue soil with pyrites, 

 1 9 Green sand. 



8 4 Leafy clay. 



