206 NEOZOIC TIME. [CHAP. XI. 



that we may assume this clay extended across the Channel 

 and into northern France. 



The Bracklesham and Bournemouth Beds form a well- 

 marked group, which is most fully developed in the Hamp- 

 shire basin. At Bracklesham in Sussex they are wholly 

 marine, consisting chiefly of clays and green glauconitic 

 sands, which yield a large rnolluscan fauna of a much 

 more tropical aspect than that of the London Clay. Num- 

 mulites appear for the first time, and are very abundant in 

 some of the beds, while Alveolina and other Foraminifera 

 enter largely into the composition of certain layers of cal- 

 careous sandstone. At Whitecliff Bay the lower part has 

 a more estuarine aspect, and at Alum Bay nearly the 

 whole is estuarine and lignitic. At Bournemouth the 

 greater part is fluviatile and freshwater, the lower beds 

 containing a large and varied assemblage of plant remains. 



Still further east, in Devon, there is a tract of lacustrine 

 beds which appears to be of the same age (Bovey Beds). 



This series is represented in the London basin by the 

 Middle and Upper Bagshot Beds, which both contain 

 marine fossils of the Bracklesham type, but are lithologi- 

 cally more like the upper part of the Bournemouth series. 

 They only occur over small areas, and their combined 

 thickness is seldom over 200 feet, which is small as com- 

 pared with that of the group in Hampshire, where the 

 total thickness is over 600 feet. 



Moreover, it is clear that this northerly attenuation is 

 due to the vicinity of a shore-line. In the middle group the 

 fossils only occur at certain horizons, and at certain localities 

 they are by no means abundant or general ; the green earths 

 are not always glauconitic, the colouring matter being fre- 

 quently carbonaceous, and removable by combustion or 

 elutriation. 1 Freshwater diatoms have been recently found 



1 Kev. A. Irving, " Geol. Mag.," 1883, p. 404, and " Quart. Journ. 

 Geol. Soc.," vol. xliii. p. 379. 



