38 Reports & Proceedings — Geological Society of London — 



exposed. The so-called 'implements' generally occur where the 

 basement bed is most crowded witli flints. 



In the speaker's opinion these chipped flints were simply the result 

 of crushing by natural forces that acted during the cutting away of 

 the Chalk, either by ice or snow before the gravels were deposited, 

 or by lateral movement in the gravels under great vertical pressure. 



Whenever a moving stone impinged on the sharp edge of a 

 stationary flint, chips would be flaked off the flint along the lines 

 of least resistance ; but when the sharp edge of the flint is turned 

 away from the impinging force no chipping will ensue. As regards 

 the direct proof that these chipped flints were IS'ature's work, it was 

 next to impossible to reproduce the conditions under which the 

 natural chipping took place, and to make observations in a gravel 

 buried under hundreds of tons of soil, ice, and snow. The speaker 

 had, however, been able to exhibit naturally chipped flints which 

 owed their character to the foundering of a mass of gravel in a pipe, 

 the gravel breaking throixgh a layer of flints in the Chalk. 



Mr. S. Hazzledine Warren, in exhibiting the results of certain 

 experiments upon flint, said that he wished to make it clear that 

 these experiments were not conducted from the point of view of 

 proving what Nature could do by the attempted simulation of natural 

 causes, but from the point of view of investigating the properties 

 of flint. What he was endeavouring to elucidate by experiment was 

 the manner in which ilint chipped when subjected to forces of 

 measured strength applied in different directions. Many methods 

 were being used, one of which was that of movement under pressure 

 of a sled which could be loaded at will with different weights. This 

 process resulted in the reproduction of the Kentish form of eolith, 

 a load of 250 lb. being sufiicient for the production of most of even 

 the larger forms. It was, however, insufficient for the reproduction 

 of the big chipping often present upon the sub-Crag flints. 



In considering subsoil pressures, in a soil of medium weight (a clay- 

 with-flints) a stone having a superficial area equal to a rectangle of 

 8 by 6J inches was under a pressure of 250 lb. at slightly less than 

 6 feet below the surface ; at a depth of 50 feet the same stone would 

 be under about nine times that pressure, while beneath 500 feet of 

 ice it would be under forty times that pressure. It was important 

 to remember that striated surfaces were associated with both the 

 Kentish ' eoliths ' and the sub-Crag flints, and these pointed to the 

 conclusion that strong movements under pressure had actually 

 operated upon the flints in question. 



Although the speaker did not wish to postulate too close an 

 analogy between experimental and natural conditions, yet if, broadly 

 speaking, the chipping properties of flint discovered by experimental 

 investigation could be relied upon as also applying under natural 

 conditions, then such chipping as was seen in the flints in dispute 

 might theoretically be expected to occur. 



A small series of chipped flints obtained from the base of the 

 Tertiary beds at Harefield was also exhibited. In this section the 

 bulbous chips could be found in the facets of the parent blocks from 

 which they had been forced away by the operation of subsoil pressure. 



