l!^ .MAHK.S OF rEIJCLSSluN <>N SlLICKoU.S KtuKS, 



It is mere than probable that the different chemical 

 compositioii of flint and hornstone produces th?se some- 

 what different features, of what must be considered one 

 and Ihc same effect cf percussion. 



CONCLUSION. 



The accessory marks above described represent tho 

 five principal mechanical effects of percussion, but it must 

 not be supposed that they always occur together in one and 

 the same specimen. In fact, so far. not a single specimen has 

 come under my notice which exhibits all of them simul- 

 taneously. The production of accessoi'y marks of per- 

 cussion is unqestionably influenced to some degree by the 

 mineralogical natui'e of the rock. The cone of percu.ssion 

 is more frequent in the porphyritic breccia and porcel- 

 lanite than in chert^ or hornstone rock; while, on the other 

 hand, the concentric wrinkles cf percussion are always well 

 defined in chert or hornstone, while hardly noticeable in 

 porcellanite or porphyritic breccia. 



The shattering of the surface is also always much 

 better shown in chert or hornstone than in any of the other 

 rocks. 



It is therefore certain that the nature of the reck 

 influences the character of the marks cf percussion. The 

 different composition must produce a different resistance 

 to the transmission of vibrations, and as a result we mav 

 anticipate the production of certain marks in preference to 

 others in certain rocks. 



But though this may be so, it is impossible to say at 

 this stage, what amount of energy was reqviired to produce 

 a certain effect. So far, all we know is that a flake, how- 

 ever large its size, was detached by a simple blow only from 

 tne parent rock. It is further very probable that failure 

 was not chielly due to insufficient energy, but probably 

 more to the hammer stone not striking the surface at the 

 critical angle of about 45deg. The intense shattering of 

 the surface which denotes the ineffective blow proves con- 

 clusivelv that the blow was admini.sterod with great force, 

 yet no flake was detached. InsuflTicient energy can, there- 

 fore, not have been the sole reason of failure ; it might be 

 argued that the ineffective blow was administered by in- 

 experienced hands ; for instance, of children. This may be 

 so or not, it only proves that these hands had not leanit to 

 direct the blow at such an angle towards the surface that 

 the energy was utilised in detaching a iiakc, and not shat- 

 tering the surface. The same may also frequently have 

 happened to older and more experienced hands. 



