A HISTORY OF KENT 



sinking rapidly through the pores and crevices of the rock, so that water 

 is stored underground in large quantity, and is obtained in abundance 

 from many deep wells. 



Toward the close of the Cretaceous period the ocean which for 

 so long had covered the greater part of the British Islands became 

 diminished in depth and extent by reason of an elevatory movement of 

 this part of the earth's crust, and finally the whole region was brought 

 once more above sea-level. This change, so far as our country is con- 

 cerned, is indicated by a gap in the geological record, since it is of course 

 only in areas where at any particular period deposits have accumulated 

 that we can read the course of events directly from the stratigraphical 

 evidence. In Kent we can only judge of the great lapse of time between 

 the deposition of the highest beds of Chalk still preserved and of the lowest 

 of the overlying formations, by the fact that in the interval a vast change 

 had taken place in the life-forms, and that every species of the Chalk 

 sea, except perhaps a few microscopic animals of low development, had 

 become extinct and had been replaced by species unknown in the 

 previous epoch. To the marine life of the present time the fossils of 

 the Chalk bear scarcely a trace of specific or even generic resemblance ; 

 but those of the immediately overlying Eocene deposits, although still 

 very different, show a distinct and thenceforward increasing relationship 

 with the existing life-forms of our seas. 



The floor of the Chalk sea appears to have been elevated so gradu- 

 ally and evenly in the south-east of England that, when it came within 

 reach of the erosive agency of waves and currents, its destruction pro- 

 ceeded at approximately the same rate over wide areas ; so that the newer 

 deposits, in part made up from its waste, were spread out upon the worn 

 surface in sheets almost parallel with the stratification of the Chalk 

 itself; and the unconformity of bedding which usually accompanies the 

 junction of rocks which differ considerably in age is rarely noticeable 

 where the lowermost Eocene beds rest upon the Chalk in the Kentish 

 sections. 



LOWER LONDON TERTIARIES 



When our stratigraphical record is resumed it indicates the exist- 

 ence of a shallow sea with shifting currents, and afterwards marks the 

 approach of the estuary of a large river probably flowing from the west- 

 ward into this sea. Under these conditions a changeful series of sands 

 and clays with pebble beds was formed, which are collectively known 

 as the Lower London Tertiaries and constitute the lowest group of 

 the Eocene period. 



Thanet Beds. — The earliest member of the group is the Thanet 

 Beds, a marine deposit of fine pale-coloured sand, often somewhat clayey 

 or loamy. This, as its name implies, is well developed in the north- 

 eastern part of the county, in the shallow trough or syncline of Chalk 

 between the Isle of Thanet and the North Downs, where it has a 

 thickness of about 60 feet, and is exposed in the cliffs of Pegwell Bay 



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