86 Art of making Gun-Flints . 
in thickness, of an earthy, chalky appearance, and loose 
texture, much softer and less heavy than the silex it en* 
velopes. The external form of the masses of good 
stones of this description has a somewhat convex sur- 
face, approaching to the globular figure. Those of ir- 
regular forms are full of imperfections. The best stones 
are not very large. They seldom exceed the weight of 
twenty pounds, and they ought not to be of less weight 
than one or two pounds. Their aspect, when broken, is 
greasy, shining a little, and the grain is so fine, that it is 
imperceptible. The colour of these good stones may 
vary from the yellow colour of honey to a blackish 
brown. In this respect it is to be noted that the value 
of a stone does not depend on its colour, but on the uni- 
formity of the tint, which becomes less intense when the 
stone is reduced into thin splinters. The flints of the 
two departments first mentioned are yellowish. Those 
of the chalk hills on the banks of the Seine are blackish 
brown. Both the one and the other, when pulverised, 
are perfectly white. The silex pyromachus ought to pos- 
sess an uniform semi-transparence, of a greasy aspect, 
to such a degree, as to admit letters to be distinguished 
through a piece of the stone of one -fiftieth of an inch 
thick, laid close upon the paper. Its fracture must be 
smooth and equal throughout, and very slightly conch- 
oidal ; that is to say, convex or concave. This kind of 
fracture is one of the most essential properties upon 
which the faculty of being divided into gun-flints de- 
pends. 
The workmen select the stones proper for their use by 
their external character. They compare that part of the 
masses of silex, which is uniformly semi-transparent and 
coloured, to the inner skin of bacon, which they call 
couenne . They say that one flint has more or less cou- 
enne, or is more or less fat than another. They assert 
