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 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every species of the Chalk sea, except perhaps a few microscopic animals of low development, had become extinct and had been replaced by species unknown in the previous epoch.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 16