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 north- 

 ern 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 Nor- 

 folk, being sections of the strata deposited in it. 



The dip of the chalk of the North Downs from Dover to Guild- 

 ford 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°.* 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 ; ivith a comparison between them and 

 those in the Basin of Farts, 



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 j but for greater 

 simplicity I shall divide the formations composing our basins into 



*For the poiuting out of this fact, as well as for much important information respecting 

 the extent of the chalk, I am indebted to G. B. Greenough, JEsq. V.P.G.S, 



