External and Internal Face only, ^ Internal Flakes, 

 original crust forms i>lane of |^ Ist order, 



Percussion and i' ' ' 

 at proximal end. 



Percussion and is if preserved! Fig. 4 and 4a. 



External, Internal, and Percus-"! Internal Flakes, 

 sion Face, original crust is if r 2ud order, 

 preserved at distal end. J Fig f). and 5a. 



14 MAKKS OF I'KUCUSSIOX ON SILICEOUS liOCKS, 



External (Iiidical) 

 Face formed Ijy 

 the plane of 

 fracture of for- 

 mer flakes : 

 II. Inteuxai. 

 Flakks. 

 (Usually distin- 

 guished by one or 

 two longitudinal 

 ridges on the in- 

 dical face.) 



External flakes of the first order are not very com- 

 mon; of this class are the most primitive types of 

 human implements produced from the fracture of siliceous 

 rocks. External flakes of the second order form the 

 great majority of the tero-watta, and they frequently 

 show a most elaborate finish of the Indical (external) face. 



Internal flakes are apparently rarer than the former ; 

 the last flake struck off the Kempton nucleus forms an ex- 

 ceedingly good type of the first order ; the second order is 

 apparently more common than the first, and all the tero- 

 ■watta, generally called knives belong to this group. 



C— ACCESSORY MARKS OF PERCUSSION ON THE 

 INTERNAL (POLLICAL) FACE. 



The accessorv marks of percussion are strictly limited 

 to the internal (PoUical) face, where they extend from the 

 internal edge of the Percussion face all over the surface up 

 to the distal edge. These are: — 



1 . The process of percussion. 



2. The cone or bulb of percussion. 



3. The concentric wrinkles of percussion. 



4. The scar of percussion. 



5. The radiating fissures of percussion. 



1. THE PROCESS OF PERCUSSION (P.P.) 



PI. II., Fig. 3. 



The process of percussion does not often occur ; if it 

 does, it invariably forms a kind of projection of the pollical 

 edge of the percussion face, as will be seen from Plate II., 

 Fi^. 3. 



