Vol. 62.] THE CLAY-WITH-FLINTS. 159 



To sum up, therefore, I conclude that the material of 

 Clay-with-Flints has been chiefly and almost entirely 

 derived from Eocene clay, with the addition of some 

 flints from the Chalk; that its presence is an indica- 

 tion of the previous existence of Lower Eocene beds 

 on the same site and nearly at the same relative level, 

 and, consequently, that comparatively -little Chalk 

 has been removed from beneath it. Finally, I think that 

 the tracts of Clay-with-Flints have been much more 

 extensive than they are now. These inferences, however, 

 do not exhaust the subject ; they do not answer all the questions 

 that we can ask about it, for there remains the question of the time 

 and manner in which this residual product was actually formed, and 

 this is by no means an easy question to answer. 



The accumulation cannot be regarded simply as the residue left 

 by the almost complete detrition of tracts of Heading Beds which 

 have gradually subsided into the Chalk, and have thereby absorbed 

 unworn and unbroken flints from that formation. The phenomena 

 are much too complicated to be accounted for in so simple a 

 manner. No doubt it is largely a residue of Reading Beds, and it 

 has sunk into the Chalk ; but this is not all. The basement-bed of 

 the Reading Group has been entirely broken up, the sands have 

 been largely eliminated from the final product, and there has been 

 an introduction of broken flints into this product. There is also 

 sufficient evidence to prove that many of these angular flints have 

 travelled from higher levels, and that there has been a moving 

 and pushing of material from higher to lower levels, the various 

 ingredients becoming mixed and kneaded together in the process. 



In order to form some conception of the conditions under which 

 this complex product has been accumulated, I think that we must go 

 back to the time when the Lower Eocene deposits had been removed 

 to a large extent, but when they still remained over very large 

 tracts outside the London and Hampshire Tertiary Basins. Such 

 were the conditions that probably prevailed during the Pliocene 

 Period. 



We know that there are some areas, such as Salisbury Plain, 

 from which nearly all remnants of the Eocene have been removed, 

 and on which very little Clay-with-Flints exists. In such a case 

 only two alternatives present themselves : either very little Clay- 

 with-Flints was ever formed, or else the greater part of it has been 

 entirely destroyed. I am inclined to think that its absence on 

 Salisbury Plain is a consequence of the removal of nearly all the 

 Eocene, before the period arrived when conditions specially favoured 

 the manufacture of Clay-with-Flints. Further, it seems to me that 

 this period was most probably that which included what is known 

 as the Glacial Epoch ; and 1 use the term included, because this 

 epoch must have been only the climax of a period during which the 

 precipitation of rain and snow must have been greater over the 

 whole of Europe than it had been before or has been since. 



I think, therefore, that we need not go back farther than to 



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