In hardly any instances of natural fracture does the surface of the splinter show any trace of its having been produced by a blow, though the violent impact of one stone upon another, by means of a fall from a cliff, or of other natural causes, might produce a splinter of the same form as if it had been struck off by a hammer. There would, however, be the mark of the blow on one face only of such a splinter, whereas in a perfectly artificial flake the traces of the blow by which each facet was produced would be discernible. On the sea-shore, natural splinters of flint, resulting from the blow of one wave-borne pebble on another, may occasionally be found, some of them having a kind of secondary working at the edges, the result of attrition among the pebbles on the shore. If a blow from a spherical-ended hammer be delivered at right angles on a large flat surface of flint, the part struck is only a minute portion of the surface, which may be represented by a circle of very small diameter. If flint were malleable, instead of being slightly elastic, a dent would be produced at the spot; but, being elastic, this small circle is driven slightly inwards into the body of the flint, and the result is that a circular fissure is produced between that part of the flint which is condensed for the moment by the blow, and that part which is left untouched. As each particle in the small circle on which the hammer impinges may be considered to rest on more than one other particle, it is |274| evident that the circular fissure, as it descends into the body of the flint, will have a tendency to enlarge in diameter, so that the piece of flint it includes will be of conical form, the small circle struck by the hammer forming the slightly truncated apex. That this is not mere theory will be seen from the annexed woodcut, Fig. 188, showing a cone of flint produced by a single blow of a hammer.[1162] [Illustration: Fig. 188.—Artificial Cone of Flint.] Sometimes, as has been shown by Prof. T. McK. Hughes, F.R.S., the sides of the cone are in steps, the inclination varying from 30° to 110°. This is probably to some extent due to the character of the blow, and the form of the hammer.