534 STEATIGRAPHICAL GEOLOGY 



Buckingham, Hertford, and Essex to near Framlingham in Suffolk, 

 where the influence of the syncline dies out and the boundary line 

 then runs northward to the west of Yarmouth. Its length from 

 Hungerford to Keculvers is about 120 miles, and its width from 

 Sudbury to Canterbury is nearly 60 miles, but this is probably 

 less than half its actual extent, the rest of the basin being concealed 

 by the waters of the North Sea. 



The Hampshire basin is much smaller, and lies in a trough 

 between the anticlinal axis of Winchester on the north and the 

 monoclinal of Purbeck and the Isle of Wight 011 the south, and its 

 extreme width is, therefore, only 25 miles, while its length from 

 Dorchester to near Worthing in Sussex is about 60 miles, with an 

 outlier at Newhaveii nearly 20 miles farther east. There is 

 evidence, however, of the original extension of the Eocene through 

 Dorset and East Devon. 



In Ireland freshwater beds of Eocene age are interstratified with 



Norfolk. London. 



Fig. 181. DIAGRAM TO ILLUSTRATE THE PRE-TERTIARY EROSION OF THE CHALK. 



6, 6. Upper Chalk. L. London Clay. 



a, a. Base of Upper Chalk. W. Woolwich Beds. 



T. Thanet Beds. 



the great sheets of basaltic lava which cover so large an area in 

 Antrim and Deny. In Scotland a similar set of lavas, also with 

 intercalated freshwater beds, attains a great thickness in the islands 

 of the Inner Hebrides (Mull, Skye, etc.). 



In Britain there is a decided unconformity between the 

 Cretaceous and Palaeogene Systems, a break which indicates a 

 considerable lapse of time and a great change of physical and 

 geographical conditions. We have seen that there are deposits 

 in France and Belgium which partially bridge over this gap, 

 and similar deposits may also have been formed in the British 

 area, but if so, they were destroyed before the deposition of our 

 lowest Eocene strata. It is now certain that large tracts of the 

 Upper Chalk have been removed from certain areas either before 

 or during the formation of the earlier Eocenes, for we cannot 

 doubt that the higher parts of the Chalk were originally continuous 

 from Hampshire to Norfolk, yet they do not now exist under the 

 London basin, and consequently the Upper Chalk, which in Sussex 



