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shire and the English Channel, occurring to a great extent at Sheppey 
and other parts of Kent, im Essex, and under different forms at 
Bagshot, Basingstoke, Guildford and other parts of Surrey; it is 
usually surrounded by chalk elevations. 
The London clay varies i thickness from 300 to 500 feet, but at 
High Beech in Essex it attains a height of 700 feet, and probably its 
total thickness may be more than 1000 feet. Nodules of an irregular, 
often ovate shape, containing a large portion of carbonate of lime, are 
interspersed through this formation. These concretions contain the 
remains of shells, mostly marine, but occasionally freshwater, which 
H. Warburton, Esq. M.P., has lately poimted out* ; often Nawtili, wood, 
the bones of turtles and crocodiles, which appear, like the flints in the 
chalk formation, to owe their origin to some organic substance ; when 
pulverized, they form the celebrated Roman cement so much used for 
building. They have been called Septaria, from having many divisions 
or septa which traverse the stone; and when filled with crystallized 
carbonate of lime and polished, make very beautiful tables and orna- 
ments. At Sheppey, radiated crystals of sulphate of barytes occur on 
the crystallized carbonate of lime, and in the centre of the clay sul- 
phate of lime is often found in radiated crystals. The cement stone 
is found in large quantities at Bognor, but not at Bracklesham. Py- 
rites, or sulphuret of iron, is picked up at Sheppey and on the shore 
at Bognor and Bracklesham, and sent to London. 
The Eocene formation has been subdivided into the three following 
divisions : the uppermost portion has been called Bagshot sand, the 
second or middle the London clay, and the lowermost the Plastic 
clay. These divisions are considered unnecessary by some geologists ; 
yet as certain shells are more abundant in one stratum than another, 
* There are no freshwater Eocene formations observable at Selsey, Bognor or Bracklesham 
Bay, like those in the Isle of Wight and other places. 
