Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/182

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172
Mr. Webster on the Strata lying over the Chalk.

Hill, in Berkshire. Its western extremity is much contracted, and seems to lie somewhere in the vicinity of Hungerford. Its north-western side is formed by the chalk hills of Wiltshire, Berkshire, Oxfordshire, Buckinghamshire and Hertfordshire. The most northern part of this boundary has not yet been well determined. On the east it is open to the sea, the coasts of Essex, Suffolk and Norfolk, being sections of the strata deposited in it.

The dip of the chalk of the North Downs from Dover to Guildford is from 15° to 10°, but in the narrow ridge of chalk called the Hog's-back, extending from Guildford to Farnham, the dip is very considerable being above 45°.[1] On the dip of the other sides I have had no opportunity of making any observations.

The depth of the chalk below the surface at London must be very considerable, since though wells have been sunk several hundred feet it has never been reached; but at a few miles south of the metropolis the chalk is frequently come to.

IV. Description of the Strata composing and contained in the Isle of Wight and London Basins; with a comparison between them and those in the Basin of Paris.

Transactions of the Geological Society, 1st series, vol. 2 plate page 0603.jpg

The authors of the French memoir, in order to obtain their general section, have collected the sections of various places; and by comparing them together have developed those alternations of marine and freshwater deposits, which are analogous to those we are now considering. I shall follow nearly the same method; but for greater simplicity I shall divide the formations composing our basins into

  1. For the pointing out of this fact, as well as for much important information respecting the extent of the chalk, I am indebted to G. B. Greenough, Esq. V.P.G.S.