The art is not wholly understood, for it perished soon after the Conquest, when iron came in; but, as far as the theory is concerned, I think I can give a tolerably satisfactory account of the process of manufacture. In the first place, the workman who makes gun-flints could probably make some of the simpler obsidian implements, which were no doubt chipped off in the same way. The section of a gun-flint, with its one side flat for sharpness and the other side ribbed for strength, is one of the characteristics of obsidian knives. That the flint knives of Scandinavia were made by chipping off strips from a mass is proved by the many-sided prisms occasionally found there, and particularly by that one which was discovered just where it had been worked, with the knives chipped off it lying close by, and fitting accurately into their places upon it. Now to make the case complete, we ought to find such prisms in Mexico; and, accordingly, some months ago, when I examined the splendid Mexican collection of Mr. Uhde at Heidelberg, I found one or two. No one seemed to have suspected their real nature, and they had been classed as maces, or the handles of some kind of weapon. [Illustration: Fluted Prism of Obsidian: the core from which flakes have been struck off] I should say from memory that they were seven or eight inches long, and as large as one could conveniently grasp; and one or both of them, as if to remove all doubt as to what they were, had the stripping off of ribbons not carried quite round them, but leaving an intermediate strip rough. There is another point about the obsidian knives which requires confirmation. One can often see, on the ends of the Scandinavian flint knives, the bruise made by the blow of the hard stone with which they were knocked off. I did not think of looking to this point when at Mr. Uhde’s museum, but the only obsidian knife I have seen since seems to be thus bruised at the end. [Illustration: Aztec Knives or Razors. Long narrow Flakes of Obsidian, having a single face on one side and three facets on the other.] Once able to break his obsidian straight, the workman has got on a long way in his trade, for a large proportion of the articles he has to make are formed by planes intersecting one another in various directions. But the Mexican knives are generally not pointed, but turned up at the end, as one may bend up a druggist’s spatula. This peculiar shape is not given to answer a purpose, but results from the natural fracture of the stone.