POPULAR SCIENCE 437 



tioned above (Science Progress, July 19 16, pp. 37-50), and 

 to decide whether the edge-flaking of the specimens illustrated 

 in figs. 1-7 is of human or natural origin. 



The first question for decision is the nature of the force 

 which has produced this edge-flaking, whether percussion or 

 pressure. The author does not consider there can be much 

 doubt that percussion has been the agent of fracture. An 

 examination of the edge-flaking reveals no evidence of the 

 effects of pressure, while all the characteristics of flaking by 

 percussion are, on the other hand, abundantly observable. 



There are no " opposing cones of pressure " such as are 

 produced when a stone is subjected to pressure between two 

 resistant surfaces, while the fissures and ripple-marks developed 

 upon the flaked areas are not such as are produced by the 

 effects of pressure. Moreover, the ridges between the flakes 

 are well marked, giving to the flaked edge a somewhat uneven 

 appearance, and it has been ascertained that this prominence 

 of the ridges between the flakes is very seldom, if ever, pro- 

 duced by pressure. 1 It seems, then, that the effects of pressure 

 may be eliminated in our inquiry as to the origin of the edge- 

 flaking of the specimens illustrated in figs. 1-6, and it is 

 also obvious that fig. 7 represents a stone edge-flaked by 

 percussion. The scope of the inquiry being thus narrowed 

 down, we may proceed to try to ascertain whether the blows, 

 which were responsible for the edge-flaking upon the specimens 

 mentioned, were delivered by human or natural agency. 



The next point to which attention is drawn is the direction 

 of the arrows which appear on each flake area of the flints 

 illustrated. It will be remembered that in the experiment in 

 which flints were subjected to the effects of fortuitous per- 

 cussion, it was found that the flakes removed from the edges 

 of the stones had been detached at divergent angles, and it 

 was pointed out that while it seemed reasonable to suppose 

 that haphazard blows would strike the edge of a flint at 

 different angles, the flakes removed by a human being, using 

 a hammer stone, would be taken off at a constant angle to 

 the edge. 2 



1 See former article, Science Progress, July 1916, pp. 48-9. 



2 The methods by which the direction of each blow removing a flake was 

 ascertained were described fully in the article mentioned, and need not be 

 recapitulated here. 



