32 



be distinguished. VVlien broken by a blow, one pecu- 

 liarity of flint is that it presents a "conchoidal frac- 

 ture." Take a nodule, give it a sharp short blow, knock 

 off a piece and examine the surface of the inner side of the 

 piece struck off, you will then perceive a series of conchoidal 

 or shell-like undulations extending in concentric waves 

 down nearly the whole length of the piece — the elongated 

 ends of the waves pointing away from the spot where the blow 

 was given (vide fig. 3). This point, too, presents a peculiar bul- 

 bous appearance, and is called "the bulb oi 'percussion" by those 

 who have given their attention to the subject, and to whom I 

 am indebted for most of the facts which I now place before 

 you. Every true flake has this " bulb of percussion " at one 

 end. Another distinguishing mark is the peculiar keeled or 

 ribbed appearance of the opposite side. 



We will suppose a trv^e flint J ack (not the spurious fellow 

 whose clever industry ought to have been turned to a better 

 purpose than to that of deceiving antiquaries), with a flint 

 nodule picked up from the sea-shore. He carries it to his 

 post of observation on the clifl", and proceeds from it to fashion 

 a weapon either for the chase, for the capture of fish, or for 

 the preparation of the skias of the animals killed. His first 

 object is to break off one end, and so get a smooth surface, 

 his next to procure as many angles as he can. Having, then, 

 obtained (we will suppose for the sake of illustration) an 

 octangular core, he proceeds with another pebble (possibly of 

 quartz, or of some other hard and tough stone) to strike off 

 the four angles (a, b, &c.,* vide fig. 1) by certain well-directed 

 blows, delivered with practised skill on the points (a. a. a. a). 

 Each of these angular pieces will then, on examination, be 

 found to present the true flake form ; there will be a keel or 

 central rib down the middle, and two or more less flat sur- 

 faces, with sharp cutting edges on each side : the part nearest 

 * Vide a Paper by S. J. Mackie, F.6.S., in the " Geol. Report.," for Jan., 1866. 



