Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/176

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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.

  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 marle. Some of the fossils of these strata strongly resemble freshwater shells: they appear to be the Cyclostoma, Planorbis, &c.
  12. Clay with gypsum.
  13. Portland oolite.