in unstable equilibrium on its point,—­looking as though the first puff of wind would bring them down.  The pillars were of porphyritic conglomerate, which had been disintegrated and worn away by wind and rain; while the great masses resting on them, probably of solid porphyry, had been less affected by these influences.  It was the most curious example of the weathering of rocks that we had ever seen.  From Penas Cargadas we rode on to the farm of Guajalote, where the Company has forests, and cuts wood and burns charcoal for the mines and the refining works.  Don Alejandro, the tenant of the farm, was a Scotchman, and a good fellow.  He could not go on with us, for he had invited a party of neighbours to eat up a kid that had been cooked in a hole in the ground, with embers upon it, after Sandwich Island fashion.  This is called a barbacoa—­a barbecue.  We should have liked to be at the feast, but time was short, so we rode on to the top of Mount Jacal, 12,000 feet above the sea, where there was a view of mountains and valleys, and heat that was positively melting.  Thence down to the Cerro de Navajas, the “hill of knives.”  It is on the sides of this hill that obsidian is found in enormous quantities.  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. 2.  Arrow-head; opake obsidian:  Teleohuacan. 3.  Knife or Razor of Obsidian; shown in two aspects; Mexico. 4.  Leaf-shaped Knife or Javelin-head; obsidian:  from Real Del Monte. 5.  Spear-head of Chalcedony; one of a pair supposed to be spears of State:  found in excavating for the Casa Grande, Tezcuco. (This peculiar opalescent chalcedony occurs as concretions, sometimes of large size, in the trachytic lavas of Mexico.)]