A HISTORY OF KENT 



ments of the earth's crust during Miocene times by which huge 

 mountain chains were upheaved in some parts and vast sheets of molten 

 lava poured out over the surface in others. In a minor but still important 

 degree these disturbances affected the whole of the south-east of England, 

 throwing the rocks into broad waves, or buckling them into sharp folds 

 such as may be seen in the cliff-sections of the Isle of Wight and of 

 Dorset. 



Although the already-described ' overstep ' of the upper beyond the 

 lower divisions of the Lower London Tertiaries indicates that the eleva- 

 tion of the Wealden dome must have begun very early in Eocene times, 

 it was probably under the influence of these great earth-movements of the 

 Miocene period that the principal uplift took place. And as we shall 

 presently see, the form that was then given to the surface is still reflected 

 in the river-systems of the county, which must have been established 

 when the outline of the land was very different from that which it now 

 presents. It was after this elevation that the chiselling of the surface 

 commenced of which the existing relief is the distant outcome. 



Once however in the interval between the Miocene uplift and the 

 present time the area must have been temporarily submerged beneath 

 the sea, as the following evidence will show. 



PLIOCENE PERIOD 



Lenham Beds. — Along the crest of the Downs from the coast above 

 Folkestone to within a few miles of Maidstone, the Chalk is capped here 

 and there with patches of rusty sand sometimes indurated into lumps 

 of ironstone. This material is usually unfossiliferous, but in two or 

 three places the hollow casts of marine shells have been found in the 

 ironstone, and these are sufficient to indicate that the deposit is of Older 

 Pliocene age, equivalent to the Diestian Beds of Belgium and to the 

 lower part of the Coralline Crag of Suffolk.' The sands appear originally 

 to have been glauconitic and full of shells, but have been slowly weathered 

 into their present condition by the percolation of surface-water through 

 them ; so that were it not for the preservation of the casts in the iron- 

 stone, from which it is possible to obtain determinable moulds of the 

 shells,* they would have been devoid of direct evidence as to their age. 

 The principal locality for these fossils is at Lenham, nine miles east of 

 Maidstone, where the sands and ironstone have sunk down into ' pipes ' 

 or deep cylindrical holes melted out in the Chalk by the solvent action 

 of the surface drainage in passing along ' water-sinks.' The fauna, which 

 is exclusively marine, comprises species of Turritella, Pyrula, Pectunculus, 

 Area, Terebratula, etc., and is believed to indicate a depth of the sea of 

 not less than 40 fathoms during the accumulation of the sands. ^ 



1 Mr. F. W. Harmer has recently expressed the opinion that the Lenham Beds are slightly older 

 than the Coralline Crag. See Quart. Joum. Geol. Sec. (1900), Ivi. 708. 



2 See C. Reid, Nature (1886), xxxiv. 341. 



3 Mem. Geol. Survey, 'Pliocene Deposits of Britain,' p. 52. 



