Cretaceous and Older Rocks in East Kent. 545 



the Jurassics of East Kent are distinctly related to the movements of 

 an axis of unrest lying to the east and north of Kent and possessing 

 alW.-S.E. alignment. 



Further west in Kent the Bobbing boring showed the sub- 

 Cretaceous surface to be composed of Oxfordian strata, as did also 

 that at Chatham Dockyard, thus demonstrating that the Oxfordian 

 outcrop pursues the same general north-westerly or west-north- 

 westerly direction for a considerable distance. 



A point of interest concerning the position of the northward limit 

 of the Corallian outcrop in East Kent may be noted. It will be 

 observed that the line passes south of Oxney andMaydensole, north of 

 Waldershare, and south of Barfreston, and then turns sharply north- 

 ward in the neighbourhood of the Snowdown sinking (between 

 Fredville and Barfreston) and resumes its general north-westerly 

 course northward of Fredville. This deflection may perhaps be due 

 to proximity with some anticlinal disturbance, but is more probably 

 the indication of a pre-Cretaceous dip-fault here, possessing a 

 westerly downthrow, which has resulted in a lateral displacement of 

 the outcrops southward on the eastern side of the fault. In this 

 connexion it is interesting to recall the anomalous dip of the Coal- 

 measures observed at the Snowdown Colliery, where, instead of a dip 

 of about 3° in a direction 35° west of south, as observed in the 

 Tilmanstone Colliery, one of 2£° in a direction 20° north of east was 

 found. It appears likely that faulting may have taken place here in 

 consequence of the occurrence of a sagging movement in the south- 

 west during deposition under isostatic conditions (see below). 



The denudation of the sub-Cretaceous surface in East Kent 

 obviously reached an advanced stage, and the area must have been 

 reduced almost to a smooth peneplain before the deposition of the 

 Wealden upon it. Probably, too, in earliest Cretaceous times the 

 peneplain was corraded to some extent by stream action prior to 

 the commencement of deposition, but not sufficiently so to produce 

 any very marked variations in level upon it. If we eliminate the 

 effects of post-Lower Cretaceous movements from the area by correcting 

 the present base of the Gault here to a datum-plane at Ordnance 

 Datum and consider the levels of the base of the Wealden in relation 

 to it, the latter is seen to present the form of a plain possessing 

 a very gentle southerly slope, the difference in level between the 

 highest and lowest points upon it being less than 200 feet. 



Seeing that in East Kent " the strata between the Oxford Clay and 

 the main limestones of the Great Oolite Series . . . appear to repre- 

 sent a continuous sequence of marine deposits", 1 and also that "the 

 deposition of clayey sediments went on uninterruptedly from 

 Oxfordian to Kimmeridgian times 'Y the advanced stage to which 

 the denudation attained is at first sight surprising, but on reflection 

 it will be seen that denudation in the north-east must have been con- 

 temporaneous with deposition in the south-west during the latter 

 part of Jurassic times. The general movement of uplift of the 

 British region in Portlandian times must have exposed to denudation 

 an area of Kimmeridge Clay fringing the Palaeozoic ridge in the 

 1 Lamplugh, loc. cit. 

 DECADE VI. — VOL. IV. — NO. XII. 3-5 



