828 . Geological Society. 



depending upon the separation of the reacting parts ; and 

 this, in certain positions, is equivalent to a reversal in the 

 sign o£ a, which thus becomes of the same sign as given in 

 the paper, Since the position for which this will occur is 

 different from what we supposed, it must be admitted that 

 the detailed algebra requires to be restated. 



Alfred W. Porter. 

 Reginald E. Gtbbs. 

 March loth, 1921. 



LXXVIIL Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 

 [Continued from p. 684.] 



May 5th, 1920.— Mr. G. W. Lamplugh, F.R.S., Vice-President, 

 in the Chair. 



T 



HE following communication was read 



A Natural " Eolith " Factory beneath the Thanet Sand.' By 

 Samuel Hazzledine Warren, F.G.S. 



The paper describes a section in the Bullhead Bed at Grays, 

 where the conditions have been favourable for the chipping of the 

 flints by subsoil pressure. There is evidence of extensive solution 

 of the Chalk beneath the Tertiary deposits, and the differential 

 movements thus brought about have occasioned much slickensiding, 

 and remarkable effects in the chipping of the flints. 



In the author's opinion the section affords the most complete 

 and conclusive evidence hitherto obtained in support of the theory 

 of the origin of the supposed Eolithic implements by purely natural 

 agencies. There are not only the simpler Kentish types, such as 

 notches, bowscrapers, and the like, but also the larger and more 

 advanced forms of rostro-carinates which are characteristic of the 

 sub- Crag detritus-bed. Careful digging enables the pressure-points 

 of one stone against another and the resultant chipping effects to 

 be studied in detail ; and in many instances the flakes removed can 

 be recovered and replaced. 



A few examples are more than merely Eolithic in character. If 

 such exceptional examples were removed from their associates, and 

 also from the evidences of the geological forces to which they have 

 been exposed, no investigator could be blamed for accepting them 

 without question as of Mousterian workmanship. Individual 

 specimens may often deceive : in order to distinguish a geological 

 deposit of chipped flints from the debris of a prehistoric chipping- 

 floor, it is necessary to base one's judgment upon fairly representa- 

 tive groups, and also to take into consideration the circumstances 

 in which they have been discovered. 



