542 STKATIGRAPHICAL GEOLOGY 



The Bracklesham Beds. In the London basin the lower 

 part of this group consists of brown laminated clays, overlain by 

 dark-green clayey sand from 12 to 20 feet thick, and succeeded by 

 a variable set of greenish sands with bands of clay, the total thick- 

 ness varying from 40 to 80 feet. These beds have yielded a few 

 fossils, Fusus longmvus, Turritella sulcifera, Cardita planicosta, Pecten 

 corneus, Ostrea flabellula, Corbula strmta, Nummulites Icevigatus, and 

 many fish teeth, Lamna obliqua, Carcharodon auriculatus, etc. 



Above the clays is a mass of sands formerly called the Upper 

 Bagshot Sand, but now referred to the Bracklesham Group, and 

 possibly representing the Boscombe Sands mentioned below. At 

 the base is a layer of small flint-pebbles, and the fine yellow and 

 white sands which succeed are the highest Eocene Beds that occur 

 in the London basin. Their thickness appears to be over 200 feet, 

 for in a boring at the Albert Asylum, Bagshot, their depth proved 

 to be 226 feet. 5 These sands contain in the upper part blocks of 

 white saccharoid sandstone, which, when weathered out, are known 

 as " grey- wethers " ; they are sometimes 10 to 14 feet long, and 3 

 or 4 deep, and they often enclose flint pebbles. Organic remains 

 are rare, but here and there are casts of shells, and about forty- 

 eight species were obtained by Mr. Monckton from the Tunnel 

 Hill cutting near Pirbright on the South - Western Eailway. 

 Among these the commonest were Rimella ritnosa, Natica patula, 

 Turritella imbricaturia, Ostrea Jlabellula, Pecten reconditus, Cardita 

 sulcata, Lucina mitis, Tellina scalaroides, and Corbula pisum. 



These beds received their name from Bracklesham Bay in Sussex, 

 where they contain marine shells throughout their extent along 

 the shore, but there are no cliffs in which they can be measured. 



. The section in Whitecliff Bay exhibits the same marine type, 

 and has been described in detail by the Rev. 0. Fisher, 6 who 

 divided the group into four portions. Mr. H. Keeping has since 

 been able to fix the limit between the Bracklesham and Barton 

 Beds more exactly, and finds it to be about 70 feet lower than 

 where Mr. Fisher placed it. Making this alteration, the thick- 

 nesses of the several parts are as follows : 



Feet. 



A. Green and blue clays with a bed of sand about 52 feet from the 



base, Nummulites variolarius, Pecten corneus, Corbula 

 pisum, Pleurotoma plebeia, etc 182 



B. Yellow sands and sandy clays, Num. variolarius ... 27 



C. Sandy clays and green sands, Num. Icevigatus, Sanguinolaria 



Holloivaysi, Valuta spinosa, etc 123 



D. Laminated clays and green sands with a bed of pebbles at the 



base, Num. Icevigatus and a few other fossils . . . 251 



583 



