TIIK KOCENE 8EKIKS 535 



is at least 750 feet thick, and in Norfolk is probably 1000 feet, 

 has only a thickness of from 250 to 300 feet beneath the valley of 

 the Thames. Moreover, where the Upper Chalk is thinnest, tin; 

 London Eocenes are thickest, and there can be no doubt that these 

 Eocenes were deposited in a broad and deep trough, which had been 

 excavated out of the Upper Chalk. The relation of this trough to 

 the general surface of the Chalk is indicated in the diagram, Fig. 181. 

 The following are the divisions of the Eocene Series now recog- 

 nised in the London and Hampshire basins. They can be grouped 

 into Lower and Upper Eocene, but the creation of a Middle 

 Eocene is quite unnecessary. 



Upper 



Lower- 



London Basin. Hampshire Basin (Isle of Wight). 



Feet. Feet. 



? Wanting. Barton Beds . 340 to 360 



Brackles- f Sands about 200 /Bracklesham and 



60 \ Bournemouth Beds 555 to 583 



150 Bagshot Beds . 243 to 98 



400 London Clay . 230 to 320 



ham \Clays 

 ^Bagshot Beds . 

 London Clay . 

 Woolwich and 



Reading Beds 

 Thanet Beds . 



80 Reading Beds . 80 to 160 



80 Absent 



About 970 1450 to 1520 



It will be seen that the Lower Eocene is more fully developed 

 in the London basin than in Hampshire and includes the lowest 

 division (Thanet Beds), which does not occur in Hampshire. On 

 the other hand, the Upper Eocene is thin and incomplete near 

 London, but is fully developed in the Hampshire basin. 



The Thanet Beds, as their name implies, are well developed 

 in the Isle of Thanet. They consist mainly of pale-coloured sands, 

 the lowest part being always argillaceous and full of dark-green 

 glauconitic grains, while at the base, and resting on the Chalk, 

 there is invariably a layer of unworn green-coated flints. These 

 flints show no signs of attrition, and are believed to have been 

 derived directly from the underlying chalk, not by mechanical 

 erosion, but by chemical solution; carbonated rain -water per- 

 colating through the sands and dissolving the subjacent chalk, 

 but leaving the insoluble flints behind ; so that a layer of these 

 nodules has gradually accumulated at the base of the sand, but 

 was not there when the sands were originally deposited. This 

 supposition is confirmed by the fact that no fossils occur in this 

 basement-bed, whereas if the flints had ever kin on a sea-bottom 

 small oysters, serpulae, etc., would certainly have fixed themselves 

 011 to such favourable surfaces for attachment. 



In East Kent the greater part of this stage consists of greenish 

 sandy marl (50 or 60 feet), overlain by sharp greenish-grey sand 



