OF MOULIN-QUIGNON. 605 



yielded by the same deposit ; and the most important jjieces 

 among the former were covered with the same matrix as the 

 latter. If either proved to be open to suspicion upon the 

 internal evidence, doubt was pro tanto reflected upon the 

 other. I shall therefore consider the evidence of the haches 

 as well as of the jaw. 



1. Intrinsic Evidence of the Haches. — And first as regards 

 the haches. Suppose a mass of a compact hard, homogeneous, 

 non-crystalline, mineral substance like Obsidian or Flint, 

 presenting a flat surface. Let a blow be struck perpendicu- 

 larly to the latter, with moderate force, by a light convex 

 iron hammer, anywhere near the centre, and an invariable 

 result follows. Although not visible externally, a partial 

 solution of continuity takes place in the interior of the 

 mass, in the form of a cone of which the point of impact 

 constitutes the apex. Suppose the mass to have the shape 

 of a polygonal block, and a similar blow to be struck 

 near the periphery, where there is a line of least resist- 

 ance, a flake will be detached; and as from the given 

 conditions there is »ot sufficient thickness of substance for 

 the vibrations being propagated uniformly all round, instead 

 of a cone, the flake presents a conoid surface, the immediate 

 apex of which above, corresponding with the point of impact, 

 is a true cone. The general convex surface which results 

 may be compared to that of one of the valves of a convex 

 bi-valve shell ; and the hollow which it leaves on the block 

 is commonly known under the name of ' conchoidal frac- 

 ture.' The phenomena have long been observed, but although 

 manifestly dependent on a definite physical cause, they have 

 not yet, so far as I have been able to ascertain, been made 

 the subject of mathematical analysis. 



Suppose the same conditions in another block, but let the 

 blows be struck with a piece of flint or other hard stone ; the 

 same effects are produced, but modified. In the one case the 

 resultant cone is more depressed, and in the other the 

 conoid convexity, ' or bulb of impact ' on the flake, is less 

 prominent and extended over a broader surface. A necessary 

 consequence is that the conchoidal facets produced by the 

 repeated detachment of flakes, or splinters, when stone-struck, 

 are broader and shallower, and the dividing ridges less ele- 

 vated ; while iron-struck facets are deeper, narrower, and 

 more pronounced, with more elevated and more angular 

 dividing ridges. I put the case in the most general terms, 

 as founded on observation. The principal cause of the 

 difference has still to be made out ; but one thing is certain, 

 that commonly the facets, upon the most ancient haches, are 

 shallower and less pronounced than in modern imitations. 



