94 SCIENCE PROGRESS 



can be established. As is well known, the leading feature of 

 this industry is the use of flake implements worked on one 

 face only, in place of hand-axes worked on both faces ; and in 

 their most typical development these flakes have the striking 

 platform facetted, and were struck off from a specially trimmed 

 block of flint, often spoken of as a " tortoise core." Where 

 then either facetted butts or tortoise cores are present, we 

 may diagnose Le Moustier with some confidence, but their 

 absence is a purely negative feature, and has but little value 

 as evidence. On the whole, Acheulean flakes are thicker and 

 clumsier, and the secondary edge-clipping is less perfect ; 

 but probably no two authorities would agree in drawing the 

 line between them. 



Messrs. Smith and Dewey were evidently not convinced 

 of the occurrence of true Le Moustier in the Wansunt clay, and 

 this, coupled with the doubt as to whether that clay really 

 belongs to the ioo ft. terrace, makes it unwise to rely on this 

 locality as proving the presence of the river at so high a level 

 in Mousterian times. Many flakes of Mousterian character 

 have been found at this altitude in other localities ; but so 

 far none of them have been traced to a definite fluviatile 

 deposit. 



One of the most prolific sources of these implements is 

 Baker's Hole, Northfleet, where a flint factory was evidently 

 established 30-40 ft. above the present river, but was after- 

 wards overwhelmed by a mass of debris, which, probably in a 

 semi-frozen state, swept down on to it from above. It is 

 evident, therefore, that at this stage of the Mousterian period 

 the river-level had already sunk far below the 100 ft. terrace. 

 The Crayford brick-earth takes us a step further, for typical 

 cores and flakes have been found underneath it at about 25-30 

 ft. above the river. 1 Now the Crayford brick-earth starts almost 

 from the river-level and reaches up almost if not quite to the 

 100 ft. terrace ; so that we have to deal with two long periods, 

 one of erosion, during which the river-level descended from the 

 100 ft. terrace almost to its present position, and another of 

 deposition, in which (assuming the brick-earth to be wholly 

 fluviatile) it rose again to about 90 ft. O.D. 3 The sheet of 

 gravel under the brick-earth contains no distinctive industry, 



1 Proc. Prehist. Soc. E. Anglia, vol. ii. pt. ii. p. 240. 



2 Proc. Geo/. Assoc, vol. xxv. (1914), p. 69. 



