FLINT FRACTURE AND FLINT IMPLEMENTS 41 



Details of Flint Fracture 



Striking Platforms. — When an ordinary nodule of flint is 

 selected with a view to produce an implement from it by 

 flaking, it is necessary, owing to the difficulty of removing flakes 

 from a rounded surface, to break off a portion of the nodule, so 

 that a flat surface is produced, upon which blows removing 

 flakes can be struck with precision. The flakes which are re- 

 moved will exhibit, in the immediate vicinity of the point 

 where the blows fell which detached them (known as " the 

 point of impact "), a portion of this flat surface, and this is 

 termed the " Striking Platform." 



The Cone of Percussion. — When a certain type of blow is 

 delivered in the centre of a flat surface of sound flint, and the 

 portions of this surface surrounding the point of impact tapped 

 gently with a hammer, these portions will generally fall away, 

 revealing a more or less perfect cone of flint. This is known as 

 " the cone of percussion," and is due to an inherent property 

 in the flint itself to fracture in this manner. This peculiar 

 method of fracture is also found to be present in some other 

 substances, such as glass, obsidian, etc. 



Positive and Negative Cones of Percussion. — When a flake 

 exhibits just below the point of impact a conical protuberance, 

 and the block from which it was struck a corresponding hollow 

 or depression, the former is known as the " positive," and the 

 latter as the " negative " cone of percussion. The detached 

 flake may as often exhibit the negative cone and the parent 

 block the positive, but that does not affect the validity of the 

 description given above. 



traillures. — If a number of flakes removed by blows are 

 examined it will be seen that many of them exhibit on their 

 bulbar surfaces (that is, the surfaces upon which the positive 

 cone of percussion is visible) a scar, where a small and isolated 

 flake has become detached. This small flake is apparently 

 removed simultaneously with the detachment of the larger flake, 

 but the exact reason for its removal does not appear up to the 

 present to have been satisfactorily explained. This eraillure or 

 1 ' mark ' ' is sometimes seen upon flakes removed by pressure (fig . 1 ) . 



Ripple Marks or Conchoidal Ripplings. — These ripple marks, 

 which are often seen upon flakes and implements of human 

 manufacture, and also upon flints flaked by fortuitous means 



