Before the conquerors introduced the use of iron, these deposits were regularly mined, and this place was the Sheffield of Mexico.
We were curious to see all that was to be seen; for Mr.Christy's Mexican collection, already large before our visit, and destined to become much larger, contained numbers of implements and weapons of this very peculiar material.

Any one who does not know obsidian may imagine great masses of bottle-glass, such as our orthodox ugly wine-bottles are made of, very hard, very brittle, and--if one breaks it with any ordinary implement--going, as glass does, in every direction but the right one.

We saw its resemblance to this portwine-bottle-glass in an odd way at the Ojo de Agua, where the wall of the hacienda was armed at the top, after our English fashion, apparently with bits of old bottles, but which turned out to be chips of obsidian.

Out of this rather unpromising stuff the Mexicans made knives, razors, arrow- and spear-heads, and other things, some of great beauty.

I say nothing of the polished obsidian mirrors and ornaments, nor even of the curious masks of the human face that are to be seen in collections, for these were only laboriously cut and polished with jewellers' sand, to us a common-place process.
[Illustration: STONE SPEAR-HEADS AND OBSIDIAN KNIVES AND ARROW-HEADS, FROM MEXICO.1.Flame shaped Arrow-head; obsidian: Teleohuacan.