160 MR. A. J. JUKES-BROWNE ON [May I906, 



Pliocene time to find Eocene deposits still occupying the greater 

 part of the region between the London and Hampshire Basins, and 

 also covering most of the ground which lies between the Chalk- 

 escarpment and the main outcrop of the Eocene along the north- 

 west side of the London Basin. Yalleys were then being cut 

 through these Eocene deposits, and some had doubtless been carried 

 deep enough to reach the Chalk : but the intervening plateaux were 

 probably so much broader, and all the minor valleys so much 

 shallower, than they are now, that the cover of Eocene was nearly 

 continuous. 



Let us next imagine the climatic changes which took place at 

 the close of the Pliocene Period and during the early part of 

 Pleistocene time. At first, there would be only an increased 

 rainfall ; but this would keep all the sands and clays of the Eocene 

 deposits in a more or less saturated condition. Later on, each 

 winter would bring heavier falls of snow, especially on the higher 

 ground, and eventually a time would come when the high plateaux 

 would be covered by thick snow-caps which might only melt off 

 entirely during three or four months of the year. 



How would such conditions affect a plateau consisting of saturated 

 Lower Eocene beds ? I think that a considerable amount of move- 

 ment would take place under the pressure of the snow-caps down 

 the dip-slopes and outward from the main anticlinal flexures. 

 Much loose sand might be pressed out from between the clays, 

 while the latter would be greatly disturbed and broken up. By the 

 general downward movement of the soil, flints from the higher 

 Chalk-ridges would be carried to lower levels, and being cracked 

 by the variations of temperature to which they must have been 

 exposed, would furnish a supply of angular flints and flint-chips 

 which would become mixed with the reconstructed Eocene material. 

 Lastly, in those places where the Eocene cover had been reduced 

 to a comparatively-small thickness of Reading Beds, these beds 

 may have been disintegrated and reconstructed down to their very 

 base : outlying tracts being completely broken up and crushed, or 

 spread out over a larger surface. 



The foregoing hypothesis, although arrived at independently, is 

 really but an amplification of an opinion already expressed by 

 Mr. Clement Reid in the following terms : — 



' Another thing must be taken into account in estimating the date of any 

 particular part of the Clay-with-Flints. It is highly probable that much of the 

 deposit was to some extent disturbed and reconstructed during the Glacial 

 Period, when floods, caused by the melting of the snow, or by rain falling on 

 frozen soil, combined with creep or soil-cap motion further to mix material 

 which had already been moved.' 1 



I only differ in thinking that the deposit was mainly formed by 

 such movement and reconstruction as took place during the Glacial 

 Epoch. 



When the Glacial episode passed away and the climatic con- 

 ditions became less severe, large tracts which had previously been 

 covered by a normal succession of Eocene deposits must have been 



1 'The Geology of the Country around Salisbury' Mem. Geol. Surv. 1903, 

 p. 64. 



