HARD WICKE'S SCIENCE-GOSSIP. 



109 



tion of the Tertiaries established by Lyell, and the 

 grounds of that classification were then briefly touched 

 upon ; and some reference was made to Prestwich's 

 Geological Map of Europe, and to Professor Zittel's 

 sketch-maps of the distribution of land and water in 

 middle and western Europe in Cretaceous and Eocene 

 times,* 



It was thus briefly pointed out how the great 

 Cretaceous sea was broken up into a number of 

 detached areas of deposition, one such area being 

 the Eocene Anglo-Gallic Basin, which included the 

 south-east of England, the north of France, and 

 Belgium ; and the data, on which our knowledge of 

 this is based, were briefly touched upon. In this 

 basin were deposited the Lower London Tertiaries ; 

 the Thanet Beds (marine) to the east ; and the 

 Woolwich and Reading Beds, with marine shells in 



First Delimitation of the Tamisian Area. 



The initiation of the movements which have taken 

 place along the line of the Kingsclere-Hindhead axis 

 was the first step towards the delimitation of the 

 Eocene Tamisian area of drainage. This may have 

 occurred in early Eocene time, since there seems to 

 be no clear evidence to show that the London Clay 

 and the Bagshot Beds of the London area were ever 

 continuous with those of the Hampshire Basin, while 

 the diminished thickness of the London Clay, where 

 it lies against the flank of the great anticlinal, and 

 underlies the Bagshot Beds * (as at Highclere), 

 points to the end of the London Clay period as the 

 forward limit (in time) for the movement referred to. 

 On the other hand the maintenance of a pretty 

 constant thickness by the Woolwich and Reading 



Aylesbury. The Chilterns 

 N i 



Windsor. 



Bagshot. 



Hog's Back. 



Hindhead. 



Fig, 84,— Digrammatic Sections through Windsor; showing probable position of Strata at end of Eocene. 



Fig. 85.— Showing probable position of Strata during Pliocene. — p g, Platean-gravcls ; b s, Bagshot Sands ; Lc, London clay ; 

 W R, Woolwich and Reading Beds ; CH, chalk ; x, formations older than the chalk. 



east Kent, with estuarine shells in West Kent and East 

 Surrey, becoming unfossiliferous, except for an 

 occasional flora (as at Reading), in Berks. The 

 evidence which these facts furnish of the drainage in 

 early Eocene time, having come from the west, was 

 dwelt upon. The numerous outliers of the Woolwich 

 and Reading Beds, and the wide distribution of the 

 sarsens and conglomerates, which we can identify 

 with them, upon the present dip-slopes of the two 

 Chalk ranges, which bifurcate towards Norfolk and 

 Dover respectively, and even beyond the present 

 principal escarpment of the Chalk (as at Avebury), 

 tell of the enormous extent of this ancient Eocene 

 estuary, which Sir Andrew Ramsay has compared, in 

 extent and importance, with the modern estuaries of 

 the Ganges and of the Amazons, t 



" Aus der Urzeit " (Oldenbourg, Munich), Tafn. iii. and iv. 

 t " Phys. Geol, of Great Britain '" (5th ed.), p. 247. 



Beds and their lithological similarity in Berks and 

 Hants, seem to tell us that no important movement 

 along the axial line occurred during the period of 

 their deposition. The small areal range of outliers of 

 London Clay on the Chalk Hills of Oxfordshire, 

 Bucks and Herts to the north, and of Hants, Berks, 

 Surrey and Kent to the south, affords another 

 indication of the diminution of the area of deposition 

 of the London Clay as compared with that of the 

 formations which preceded it. 



As is often seen to be the case, these initial move- 

 ments on the southern line of elevation, and probably 

 movements on a Mercian line of elevation also, had 

 their counterpart in a corresponding depression of 

 the intermediate synclinal, which was gradually 

 filled with the sedimentary deposits, whose accumu- 

 lations have given us the London Clay. 



• "Journal of the Geol. Soc," loc. supra cU. 



