§ 27. LONDON CLAY OF HAMPSHIRE. 239 



on the strata above the English Chalk, formed a new era 

 in British Geology, and raised our tertiary series to an im- 

 portance equal to that of the Paris basin. 



" The clays and sands of Alum Bay afford one of the most interest- 

 ing natural sections imaginable. They exhibit the actual state of the 

 strata above the chalk, before any change took place in the position 

 of the latter. For, although the beds of which they are composed are 

 quite vertical, yet, from the nature and variety of their composition, 

 and the regularity and number of their alternations, no one who views 

 them can doubt that they have suffered no change, except that of 

 having been moved with the chalk from a horizontal to a vertical 

 position. These sands and clays present every variety of colour of 

 green, yellow, red, crimson, ferruginous, white, black, and brown." 



27. London clay of the Hampshire basln. — The 

 London clay extends over the greater portion of the area 

 of the Hampshire basin, its peculiar fossils abounding in 

 many localities. Castle Hill, near Newhaven, which has 

 been already mentioned as an isolated portion of the 

 lower series of plastic clay, is made up of sands, marls, and 

 clays, with beds of oyster-shells and shingle ; these deposits 

 form the upper part of the hill, and rest upon the chalk of 

 which the lowermost fifty feet of the cliff are composed.* 

 The subsulphate of alumine,^ a mineral peculiar to this lo- 

 cality, occurs in the ochraceous clay which is in immediate 

 contact with the chalk. Selenite, or crystallized gypsum, 

 abounds in the marls ; and there is a layer of surturbrand, or 

 lignite, a few inches thick, containing impressions of dico- 

 tyledonous plant s.J The clays abound in marine and fresh- 

 water shells ; some of the layers being aggregations of com- 

 pressed shells, held together by argillaceous earth. § The 



* See Geology of the South Downs, p. 261. 



f British Mineralogy, Tab. 499. Geology of the South-East of 

 England, p. 56. 



+ Fossils of the South Downs, PI. viii. figs. 1, 2, 3, 4. 



§ Two species of Potamides, and one of Cyclas, (both fresh-water 

 genera,) are the prevailing forms. 



