A HISTORY OF KENT 



of the county the borings indicate two or three thousand feet of strata 

 of intermediate age. 



Where the uppermost Jurassic beds are preserved they show that 

 after the deposition of the Kimeridge Clay, which appears to have 

 accumulated in waters of some depth, the sea became shallow and its 

 bottom covered with sand (' Portlandian '), and at a later stage ('Pur- 

 beck Beds ') its site was occupied by lagoons of brackish water through 

 the increasing influence of the rivers draining from the land ; until finally 

 the freshwater Wealden conditions were established, under which the 

 older surface rocks of the county were accumulated, as previously 

 described. 



The northward overlap of the freshwater Wealden deposits across 

 the boundaries of the marine Jurassic series, and the further overlap 

 of the Gault and Chalk across the limits of both, are proof that the 

 relative uplift of the northern district must have been repeated at 

 several stages before the deposition of the Chalk. But after the great 

 Upper Cretaceous subsidence the axis of main uplift was shifted farther 

 southward ; and as already shown, the Wealden anticline was raised over 

 the tract in which the Jurassic and Lower Cretaceous rocks had attained 

 their greatest thickness.' The pressure which caused the upward bulging 

 of the Wealden dome appears to have acted laterally from the south, 

 the thick masses of yielding Secondary sediments, confined by the rigid 

 Palaeozoic slope on the north, obtaining relief from the compression by 

 broad undulation. 



In this glimpse at the foundation rocks of the county we have been 

 enabled to trace the outlines of its evolution backward to the remoter 

 periods of geological time. But it must be remembered that in other 

 regions there are rocks now exposed at the surface of far higher antiquity 

 than the oldest of those reached by the deep borings in Kent, and that 

 although our records have covered a past that is immeasurable by any 

 time-standard within our grasp, they yet fail by many sons to reach 

 backward to the known limits of geological time. The Palaeozoic 

 sediments of Kent must themselves have had a floor on which to rest ; 

 and our knowledge is bounded only by the limitations of our researches. 



1 As pointed out by Topley {Quart. Journ. Geol. Soc. xxx. 1 86, and 'Geology of the Weald,' 

 p. 241), the Wealden dome may have been in part built up by this thickening of the Secondary rocks 

 toward its centre, independently of the effect afterwards produced by unequal uplift. 



