158 me. a. J. jukes-beowne osr [May 1906, 



sandstone, in fact all the components except the unworn flints, could 

 be, and probably were, furnished by the Reading Beds. 



A study of the stratigraphical relations of the two deposits shows 

 that the largest and most frequent tracts of Clay-with-Flints are 

 almost always found at levels which approximate to the prolon- 

 gation of the inclined surface on which the Eocene lies ; and, where 

 they are at a distance from the main outcrop of the Eocene, the 

 positions which they occcupy are generally those where traces and 

 remnants of Reading Beds might be expected. 



Again, the larger tracts of Clay-with-Flints frequently border or 

 support masses of brickearth and loam which have evidently been 

 formed out of the wreck and disruption of Reading Beds. Lastly, 

 existing outliers of Reading Beds are often flanked or bordered by 

 Clay-with-Flints, which sometimes passes from the surface of the 

 Chalk onto that of the Eocene ; there are also cases in which 

 several outliers of Reading Beds are united into one connected tract 

 by a broad spread of Clay-with-Flints. 



I do not, of course, deny that some of the contents of this clay 

 have been derived from the Chalk ; the larger unbroken flint- 

 nodules must have come from this source, and in most cases this is 

 probably a consequence of the solution of chalk in situ ; but I 

 maintain that the amount of clay that can have been derived from 

 the Chalk must have been very small, because it can generally be 

 proved that only a small thickness of chalk can actually have been 

 destroyed since the Eocene cover was broken up and removed* 

 Thus, wherever outliers of Reading Beds occur among tracts of 

 Clay-with-Flints, or wherever the inclination of the surface on 

 which the Eocene rests can easily be prolonged as a reference- 

 datum, it is found that the base of the Clay-with-Flints is not 

 generally far below the level which must formerly have been 

 occupied by Reading Beds. Here and there small quantities of 

 Clay-with-Flints may have been let down by landslips, or have 

 subsided into pipes and hollows, but the tracts of it which cover 

 long ridges and plateaux are seldom found to be more than 30 or 

 40 feet below the datum above-mentioned, whenever an estimate 

 can be made. 



It may be objected that Clay-with-Flints does not always lie only 

 on the summits of ridges or plateaux, but sometimes occurs on one 

 side of a ridge, or irregularly on the slopes of a ridge. This is true, 

 but I think that in all these cases it has either slipped down from 

 its original level, or has been let down by solution and subsidence, 

 and that such displacements have taken place during the carving- 

 out and widening of the valleys at the expense of the intervening 

 ridges. This process of valley-erosion must have gone on rapidly 

 when the rainfall was greater than it is now, especially while the 

 Glacial Epoch was passing away. The chalk exposed along the 

 sides of the valleys must have yielded both to chemical solution 

 and to mechanical erosion by the water flowing off the ridges ; and 

 extensive landslips may have occurred in many places, by which a 

 capping of Clay-with-Flints would be carried down far below its 

 normal level. 



