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 THE 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.
Even then, the way of making several implements or weapons is not entirely clear.