42 SCIENCE PROGRESS 



(they appear to be more prominent and frequent upon the 

 latter), are due to the tendency of flint under certain conditions 

 to fracture in a conchoidal or shell-like manner. It seems that 

 these conchoidal ripplings are somewhat analogous to the 

 ripples produced upon a surface of water when some heavy 

 object is thrown on to it. The water is " jarred " by the 

 impact and ripples produced, and it may be that certain blows 

 jar the flint and so produce ripplings on the fractured surface. 

 Conchoidal ripplings are sometimes formed when a flint is 

 fractured by pressure. 



Fissures. — If a series of flakes is examined it will be noticed 

 that their surfaces exhibit a series of fissures of varying length 

 and width, which radiate from the point of impact. Some of 



Fig. i. 



these markings are easily visible to the naked eye, while others 

 require a strong lens to discern them. It seems that their 

 presence can be accounted for by supposing that when the flake 

 is removed the flint is in a sense torn and that these markings 

 represent the tears produced by the cleaving effect of the blow. 

 Fissures are sometimes produced upon a flint which has been 

 fractured by pressure. 



Truncated Flakes. — When the manufacture of a flint imple- 

 ment is commenced, large flakes are removed from the nodule 

 of flint, which in the further process of flaking get reduced in 

 size or truncated. Thus it is possible to observe the remains 

 of flakes which have been thus reduced in size on various 

 portions of the surfaces of many implements. These flakes are 

 termed " truncated flakes." 



Opposing Cones of Percussion. — Under certain conditions a 



