274 
THE GEOLOGIST. 
after, an Englishman who had lived many yea,rs at the Real offered to take us 
out for a day's ride ; and the Company's Administrador lent us two of his own 
horses, for the poor beasts from Pachuca could hardly have gone so far. The 
first place we risited was Penas Cargadas, the ' loaded rocks.' Riding through 
a thick wood of oaks and pines, we came suddenly in view of several sugar- 
loaf peaks, some three hundred feet high, tapering almost to a point at the 
top, and each one crowned with a mass of rocks which seem to have been 
balanced in unstable equilibrium on its point — looking as though the first puff 
of wind would brin^ 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 cui-ious example of the weathering of rocks 
that we had ever seen. Prom Penas Cargadas we rode on to the farm of Gua- 
jalote, 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, twelve thousand 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 Mexicb. 
" We were curious to see aU that was to be seen ; for Mr. Chi'isty's excellent 
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 port-wine 
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, which turned out to be chips of obsidian. Out of this rather unpro- 
mising stuff [he Mexicans made knives, razors, arrow- and spear-heads, and 
other things of great beauty. I say nothing of the polished obsidian miiTors 
and ornaments, nor even of the cuiious 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. 
Cortes found the barbers at the great market of Tlatelolco busy shaving the 
natives with such razors, and he and his men had experience of other uses of 
the same material in the flights of obsidian-headed arrows which ' darkened the 
sky,' as they said, and the more deadly wooden maces stuck all over with 
obsidian points, and of the priests' sacrificial knives too, not long after. These 
things were not cut and polished, but made by chipping or cracking off pieces 
from a lump. This one can see by the traces of conchoidal fracture which they 
all show. 
" 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 
