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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 originally 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.
- Alluvium, consisting of gravel, loam, sand, &c. and forming the surface or soil.
- Sand seen chiefly in the neighbourhood of Bagshot.
- Blue clay, with septaria and marine fossils, commonly called the London clay.
- Sand, plastic clay, &c.
- Chalk with flints.
- Chalk without flints.
- Chalkmarl, including what is called the grey chalk.
- 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.
- Blueish black marl.
- 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.
- A series of strata of shelly limestone, known by the name of the Purbeck stone, alternating with shale and marle. Some of the fossils of these strata strongly resemble freshwater shells: they appear to be the Cyclostoma, Planorbis, &c.
- Clay with gypsum.
- Portland oolite.
