SECTIONAL TRANSACTIONS.— C. 353 



13. Mr. S. W. WooLDRiDGE. — The Diestian Transgression in the Ixindon 



Basin and its Effect on the Geo-morphology of the North Downs 

 and Chiltern Hills. 



At the Southampton Meeting the writer presented the results of work on the 

 high-level Pliocene deposits in the central tracts of the London Basin. These were 

 represented as slightly younger than the Lenham Beds and derived in part from 

 the breaking down of the latter. 



Further work shows that we may regard the Diestian sea as having been roughly 

 co-extensive with the present London Basin as defined by the chalk escarpments. 

 Diestian outliers are far more numerous on the North Downs than is generally 

 recognised, and in all cases they rest on a wave-cut platform inclined gently north- 

 wards. Where the coastline lay south of the present escarpment, as in East Kent, 

 this platform bevels the escarpment crest. In the area south of London, however, 

 the coastline bent northward where the Downs are highest, and here the platform 

 is a bench cut in the dip-slopo and backed by higher ground near the escarpment 

 crest. This higher ground is covered with relict masses of Blacliheath Beds which 

 clearly have never been disturbed by the waves of the Diestian sea. It is concluded 

 that the low northward gradient of the Diestian base precludes the idea of any 

 pronounced re-doming of the Weald in PUocene times. The gradient is so low that 

 it may be in great part original. A method of distinguishing any such original 

 gradient, from the effects of subsequent tilting, wiU be indicated. Further, there was 

 transverse warping of pre-Dicstian date, but since the deposition of the Lenham Beds 

 there has been no resumption of that movement. 



The bearing of the facts elicited on the general problem of the denudation of the 

 Weald and the amount of recession of the chalk and Eocene escarpments since 

 Diestian times is also discussed. 



The relations of the Lenham Beds on the Chiltera Hills are found to be closely 

 similar to those displayed on the North Downs. Owing to severe glaciation and a 

 consequent higher degree of dissection, the beds are not so fuUy preserved, but 

 their existence can be demonstrated at many places. Moreover, by studying the 

 profile of the inter-consequent ridges it can be shown that the Diestian bevel or 

 bench is conspicuous throughout the area. As in the case of the North Downs, the 

 Lenham Beds are absent from the highest parts of the dip-slope, the coasthne lying 

 to the south of the escarpment crest from the neighbourhood of Princes Risboro' 

 eastwards to the Hitchin Gap. The data lend themselves to the same treatment as 

 that apphed in the case of the North Downs ; longitudinal and transverse warping 

 can be evaluated and the recession of the Eocene escarpment traced. 



Attention wiU be directed to the possible westward extension of the Diestian 

 gulf or channel and the general palaeogeography of this phase of Pliocene time wiU be 

 discussed. 



14. Dr- George Slater. — The Structure of the Disturbed Deposits of 



Mozns Klint and Lonstrup, Denmark. 



Moens Klint. — The classical disturbances of Moens KUnt extend for a distance 

 of about four miles. 



The disturbances may be divided into two groups, one north and the other south, 

 separated by a basin of chalk containing drift. In each group the structure of the 

 disturbed beds shows a localised and definite relationship to a nucleus or ' core ' of 

 chalk of asymmetrical or drumloid form, the two cores being referred to as the 

 Slotsgavlene core to the north, and the Dronningestol to the south. Owing to the 

 progressive moulding of lenticles of chalk over and against the flanks of the cores, 

 these were ultimately converted into ' horsts.' Hence there is a development of 

 thrust-planes in the beds flanking the limbs, these thrust-planes being associated with 

 drift intercalated in the chalk. To the south of the Dronningestol area the thrust- 

 planes are associated with seven squeezed chalk anticlines, each averaging 200 feet in 

 height. 



Fossil evidence proves that the transported chalk had been derived from more than 

 one zone. The disturbances are local and superficial, and the structure agrees in 

 principle with that of the Ipswich sections described at the Toronto Meeting, 1924, 

 under the title ' Glacial Tectonics as reflected in Drift Deposits.' This type of 



1926 A A 



