38 SMITHSONIAN INSTITUTION 



railroad, with which it is connected hy a small branch. Situated in a 

 broad open valley surrounded by low hills, its green trees, the blue 

 domes of its churches, and the whitewashed adobe houses give it a 

 pleasing and restful aspect. The city of Charcas was founded in 1574, 

 the rich silver veins in the vicinity attracting early attention. It was 

 also an important stage stop. On the walls of the old stage station 

 can still be discerned in faint characters the destinations of the 

 stages and distances of the stations to points as far away as Cali- 

 fornia. It is said that Cortez once made this his stopping place. The 

 mines, once worked for silver, are now more valuable as producers 

 of lead, zinc, and copper. The principal mine. Tiro General, situated 

 a few miles west of town at the base of a low range of hills, is one of 

 the great producing mines of Mexico. Copper and lead-zinc-silver ores 

 are both mined ; the ores occur at or near the contact of a porphyry 

 and limestone. Old accounts describe the number of mine workings 

 in the district as innumerable but by far the greatest number of them 

 are shallow and appear to be of little economic importance. Antimony, 

 mercury, and tin are also found in minor quantities in the surrounding 

 hills. Caves containing old Indian remains are occasionally discovered 

 in the surrounding region and I had an opportunity of visiting one 

 recently discovered from which skeletal material and a few shell orna- 

 ments and similar material were recovered. 



Between Charcas and San Luis Potosi the character of the country 

 changes abruptly from an area characterized by steep and rugged 

 limestone mountains to one of the flat-topped ridges of old rhyolitic 

 lava flows. Vegetation, too, becomes more abundant, the most con- 

 spicuous forms being candelabria and organ cacti. The lava flows 

 contain minor deposits of tin and topaz but the more important ore 

 deposits are still largely confined to the limestone rocks. 



Fifteen miles east of the city of San Luis Potosi is the mining camp 

 of San Pedro, another ancient camp discovered in the latter part of 

 the sixteenth century. The richness of its mines gave it at one time 

 the name Potosi, which was afterwards applied to the entire state. 

 The district lies in a comparatively low range of barren mountains. 

 The slopes of the mountains show abundant evidences of intensive 

 mining operations ; in places large blocks of the mountain side have 

 collapsed into the old mine workings. The ore bodies lie along fault 

 planes in limestone with porphyry in close proximity. The rich ores 

 for which the district was famous appear to be largely mined out, the 

 only evidence of their former presence being the huge underground 

 chambers from which the ore seems to have been totally removed. 

 Mining operations are at present confined to a large, recently devel- 



