144 ME. A. J. JTTKES-BROWNE ON [May I906, 



deposition of the Eocene beds upon it; so that, when viewed as a 

 whole, the Eocene strata are entirely unconformable to those of the 

 Chalk. Thus the local base of the Eocene Series rests in different 

 districts on different portions of the Upper Chalk, from the zone of 

 Belemnitella mucronata to that of Micraster cor-anc/uinum, and it is 

 very probable that (in some places) it rested on the zone of Micraster 

 cor-testudinarium, if not on that of Bolaster planus. In other words, 

 the surface which received the Eocene deposits was a surface which 

 had been planed across a raised and broadly-curved or flexured mass 

 of Chalk. 



Eurther, in one part of the region, namely in Surrey and Kent, 

 elevation and erosion seem to have been renewed in early Eocene 

 time, for Mr. Whitaker has shown ] that the Oldhaven and Black- 

 heath Beds overstep both the Woolwich and Thanet Beds, so as to 

 rest upon the Chalk. This may have taken place over a large area 

 in the northern part of the "Weald, when the Chalk extended much 

 farther south than it does now. 



Lastly, it is well known that both Chalk and Eocene were sub- 

 jected to still greater disturbance in Miocene and Pliocene times, 

 along lines that were more or less parallel to the great post- 

 Oligocene flexure of the Isle of Wight. I think it almost certain 

 that the flexuring which took place before Eocene times was of slight 

 intensity ; and that only a broad and low geanticline was then pro- 

 duced, the curvature of which included, not only the space between 

 the London and Hampshire Basins, but also part of the London 

 Basin itself : the more pronounced flexures which occur within this 

 geanticline being wholly or mainly of post-Oligocene date. 



These later flexures have a peculiar arrangement, occurring as 

 discontinuous periclines, that is, as local elliptical domes and basins 

 which are not always arranged along axial lines, but often alternate 

 en echelon, the termination of one periclinal convexity passing 

 below the beginning of a cymboid basin, or trough, which is flanked 

 on each side by elongate convex periclines, all of them dying out 

 again within a certain distance. Such an arrangement of flexures 

 is found, for instance, in the country between Winchester and Salis- 

 bury. The Kingsclere tract is another notable instance of a convex 

 pericline. 



Now, if the Clay-with-Flints has no special relation to the Lower 

 Eocene beds, but is a residue from the Chalk, the largest tracts of 

 this argillaceous residue should occur over the domes and convexities 

 which have been exposed to the greatest amount of quiet subaerial 

 detrition since Eocene time ; and the smallest and thinnest should 

 lie in the synclines from which less chalk has been removed. On the 

 other hand, if the Clay-with-Elints is mainly composed of residue 

 from the basal Eocenes let down into the Chalk, it will naturally 

 be in greatest force over those tracts from which the least amount 

 of chalk has been removed, and on which traces or outliers of the 

 Eocene deposits still remain ; while it will be entirely absent from 



1 Quart. Joura. Geol. Soc. vol. xxii (1866) p. 420; and Mem. Geol. Surv. 

 vol. iv (1872) p. 240. 



