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



the same cause, and at the same time ; and favours the idea, that 

 many of these, although now broken and unconnected, were origi- 

 nally continuous. 



A part of the series which I deduced from observations made in 

 the south-eastern part of England, is as follows, beginning with the 

 uppermost. 



1 . Alluvium, consisting of gravel, loam, sand, &c. and forming 

 the surface or soil. 



2. Sand seen chiefly in the neighbourhood of Bagshot. 



3. Blue clay, with septaria and marine fossils, commonly called 

 the London clay. 



4. Sand, plastic clay, &c. 



5. Chalk with flints. 



6. Chalk without flints. 



7. Chalkmarl, including what is called the grey chalk. 



8. Sandstone with green earth and mica, cemented together by 

 calcareous matter, and containing subordinate beds of limestone and 

 chert. This includes the firestone of Ryegate, and Kentish rag. 



9. Blueish black marl. 



10. Sand and sandstone, highly ferruginous, containing subordinate 

 beds of clay, fullers earth, shale, bituminous wood, and limestone. 

 This stratum forms the wealds of Kent and Sussex. 



11. A series of strata of shelly limestone, known by the name of 

 the Purbeck stone, alternating with shale and marie. Some of the 

 fossils of these strata strongly resemble freshwater shells : they ap- 

 pear to be the Cyclostoma, Planorbis, &c. 



12. Clay with gypsum. 



13. Portland oolite. 



I 



