26 LONDON DISTRICT. 



indicate a thickness of 391 ft. beneath Claygate and Bagshot 

 Beds; another at South Weald 37 1| ft. beneath Claygate Beds 

 only. 1 On the south side we find about 400 to 450 ft. at Esher, 

 430 ft. at Wimbledon, less than 400 ft. at the Crystal Palace, 

 and probably not much more than 300 ft. at Shooters Hill. 

 Under London the formation has undergone much erosion, and 

 the thickness met with at Tottenham Court Road (Meux's 

 Brewery) was only 63 ft., at Leicester Square 148 ft., Pall Mall 

 120 ft. and in the City 85 to 130 ft. 



Extensive lists of animal and plant remains from the London 

 Clay have been published from time to time. They include 

 many species of shells, crustaceans, fish, crocodiles, birds, and 

 mammals. In some localities plants of a sub-tropical character, 

 such as Magnolias and Ginkgo, have been found. 



The Basement Bed affords evidence of near -shore conditions, 

 and in it the slender, gently -curved tubes of Ditrupa are 

 abundant. The main mass contains shells indicative of rather 

 deeper water, such as Nautilus ; and with the return of shallow- 

 water conditions we have the transition to the Bagshot Sands 

 marked by the Claygate Beds. 



Very little detailed work has been done, however, in dividing 

 the formation into zones, according to the distribution of fossils. 

 As early as 1854 Prestwich noted four zones, but they were to 

 some extent topographical, as Sheppey and Highgate were 

 classed as first and second zones respectively, Primrose Hill, 

 Islington and other places were included in the third zone, while 

 his fourth zone included the Basement Bed. 



In the Basement Bed, the univalves Aporrhais sowerbyi 

 (Mantell) with its obliquely-ribbed spire and well-expanded 

 outer lip, the globular Natica labellata Lamarck, and the pear- 

 shaped Pyrula nodulifera G. B. Sowerby, ornamented with a 

 row of obtuse nodules on the angle of the whorl, are commonly 

 found. The bivalves of the bed include the stout, orbicular, 

 moderately-inflated Dosiniopsis bellovacensis (Deshayes) [= Mere- 

 trix orbicularis Edwards], Panopea intermedia (J. Sowerby), a 

 gaping, oblong shell, Pectunculus brevirostris J. de C. Sowerby, 

 a fairly large species, distinguished by its slight obliquity, the 

 small form of Protocardia plumstediana (J. Sowerby emend.) 

 [= Cardium laytoni Morris], an oblique, sub-trigonal shell, with 

 surface occupied by numerous flattened ribs, which are more 

 distinct on the angular side, and Ostrea bellovacensis Lamarck. 



Fossils are not regularly distributed in the main mass of the 

 London Clay; in certain exposures it is almost barren. Shells 

 are the most usual among the fossils ; specimens of Nautilus are 

 occasionally conspicuous on account of their iridescence. Uni- 

 valves occur in great variety; we find specimens of Cassis, the 

 helmet-shell, Phorus (Xenophora), one of the group of carrier- 

 shells, which become covered with bits of stone and other 



1 ' Water Supply of Essex ' (Mem. Geol. Surv.), 1916, p. 105. 



