212	NATURAL HISTORY OF GEMS.
	arrow-heads in flint so truly made, so exactly balanced, must have been produced by some similar application of a softer medium : it is found impossible to reproduce their make with any degree of perfection by modern tools. These Obsidian laminas, adds Ximenes, being mounted as an edge to a wooden sword, furnished a most terrible weapon, capable of cutting a man in twain, nay more, of slaying a horse, by a single blow, after which, however, it became useless. Another volcanic product, in great request with the later Egyptian engravers, was a Trachyte, exactly resembling Black Jasper, with which it is always now confounded, though distinguishable by its levity and bubbly texture. The exclusive employment of this Trachyte for talismanio subjects inclines me to recognise in it Pliny's Antipathes, " black and not translucent,—recommended by the Magi as a protection against witchcraft."