chaco de la Variga de Plata. They began to work these veins, which were poor and inconstant in their produce. In 1778, Don Barnabé Antonio de Zepeda, a miner of the Ojo del Agua de Matchuala, went over during three months, this group of arid and calcareous mountains. After attentively examining the ravins, he was fortunate enough to find the crest or surface of the veta grande, on which he immediately dug the pit of Guadalupe. He drew from it an immense quantity of muriated silver, and colorados mixed with native gold; and he gained in a short time more than half a million of piastres*. From that period, the mines of Catorce were wrought with the greatest activity. That of Padre Flores alone produced in the first year 1,600,000 piastrest; but the vein only displayed great riches from 50 to 150 metres of perpendicular depth. The famous mine of Purissima belonging to Colonel Obregon, has scarcely ever ceased since 1788, to yield annually a net profit of 200,000 piastres§; and its produce in 1796 amounted to 1,200,000 piastres, while the expences of working did not amount to more than 80,000. The vein of Purissima, which is not * 109,383 sterling. Trans. + Upwards of 350,000 sterling. Trans. the same with that of Padre Flores, sometimes reaches the extraordinary extent of 40 metres* ; and it was worked in 1802, to the depth of 480 metrest. Since 1798, the value of the minerals of Catorce has singularly diminished; the native silver is now rarely to be seen; and the metales colorados, which are an intimate mixture of muriated silver, earthy carbonated lead, and red ocre, begin to give place to pyritous and coppery minerals. The actual produce of these mines is nearly 400,000 marcs of silver annually.‡ The mines of Pachuca, Real del Monte, and Moran, are highly celebrated for their antiquity, their wealth, and their proximity to the capital. Since the beginning of the eighteenth century, the vein of la Biscaina, or Real del Monte, has alone been wrought with activity. The working of the mines of Moran was only resumed within these few years; and the mineral depository of Pachuca, one of the richest of all America, has been wholly abandoned since the terrible fire which took place in the famous mine del Encino, which alone furnished more than 30,000 marcs of silver annually§. The wooden work which supported the roof * 131 feet. Trans. 262,526 lib. Troy. Trans. of the galeries was consumed by fire, and the greatest number of the miners were suffocated before being able to reach the pit. A similar conflagration in 1787, put a stop to the working of the mines of Bolaños, which were only again begun to be cleared out in 1792. The valley of Mexico is separated from the basin of Totonilco el Grande, by a chain of porphyritic mountains, of which the highest summit* is the peak of the Jacal, elevated according to my measurement with the assistance of the barometer, 3124 metres† above the level of the sea. This porphyry serves for base to the porous amygdaloid, which surrounds the lakes of Tezcuco, Zumpango, and San Christobal. It seems to be of the same formation with that, which in the road from Mexico to Acapulco, immediately covers the granite between Sopilote and Chilpansingo, near the village of Acaguisotla, and l'Alto de los Caxones. To the north east of the district of Real del Monte, the porphyry is at first concealed under the columnar basalt of the farm of Regla, and farther on in the valley of Totonilco, under beds of secondary formation. The Alpine limestone of a greyish blue, in which is the famous cavern of Danto, called also the pierced moun *See my Nivellement Barometrique, p. 40-42 n. 290---312. +10,248 feet. Trans. tain, or the bridge of the Mother of God*, seems to repose immediately on the porphyry of Moran. It contains near the Puerto de la Mesa, veins of galena, and we find it covered with three other formations of not so old an origin, which naming them in the order of their superposition, are the Jura limestone, near the baths of Totonilco, the slate-free-stone of Amojaque, and a gyps of secondary formation mixed with clay. The position of these secondary rocks which I carefully observed, is so much the more remarkable, as it is the same with that which has been discovered in the Old Continent, according to the excellent observations of M. M. de Buch and Freiesleben. The mountains of the district of mines of Real del Monte, contain beds of porphyry, which with respect to their relative antiquity, differ a good deal from one another. The rock which forms the roof and the wall of the argentiferous veins, is a decomposed porphyry of which the base sometimes appears clayey, and sometimes analogous to the splintery hornstone. The presence of hornblend is frequently announced, merely by greenish stains intermingled with common and vitreous felspar. At very great elevations, for example, in the beautiful forest of oak and pine of Oyamel, we Puente de la Madre de Dios. find porphyries with a base of pearled stone, containing bedded and reniform obsidian (en couches et en rognons). What relation exists between these last beds, which several distinguished mineralogists consider as volcanic productions, and the porphyries of Pachuca, Real del Monte, and Moran, in which nature has deposited enormous masses of sulfuretted silver and argentiferous pyrites? This problem which is one of the most difficult in geology, will only be resolved when a great number of zealous and intelligent travellers, shall have gone over the Mexican Cordilleras, and carefully studied the immense variety of porphyries which are destitute of quartz, and which abound both in hornblend and vi treous felspar. The district of mines of Real del Monte, does not display as at Freiberg in Saxony, Derbyshire in England, or as in the mountains of Zimapan and Tasco in New Spain, a great number of rich veins of small extent, on a small tract of ground. It rather resembles the mountains of the Hartz, and Schemnitz in Europe, or those of Guanaxuato and Potosi, in America, of which the riches are contained in a few mineral depositions of very considerable dimensions. The four veins of Biscaina, Rosario, Cabrera, and Encino, run through the districts of Real del Monte, from Moran |