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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 Jura limestone, near the baths of Toto. nilco, the slaty limestone of Amojaque, and a gypsum 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 on 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 splintery hornstone. The presence of hornblende 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 pearlstoné, containing obsidian in layers and nodules.

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 : 1 of sulphuret of 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 hornblende 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 size, 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

and Pachuca, at extraordinary distances, without changing their direction, and almost without coming in contact with other veins which traverse or derange them.

The veta de la Biscaina of less considerable dimensions, but perhaps still richer than the vein of Guanaxuato, was succesfully wrought from the sixteenth to the beginning of the eighteenth century. In 1726 and 1727, the two mines of Biscaina and Xacal, still produced together 542,700 marcs of silver.* The great quantity of water which filtrated through the crevices of the porphyritic rock, joined to the imperfection of the means of drawing it off, compelled the miners to abandon the works when they were yet only 120 metrest in depth. A very enterprising individual, Don Joseph Alexandro Bustamente, was courageous enough to undertake a level near Moran; but he died before completing this great work, which is 2352 metres f in length from its mouth, to the point where it crosses the vein de la Biscaina. The direction of this vein is hor. 6; and its inclination is 85° to the south ; its extent is from four to six metres. S The direction of the porphyry of this district is generally hor. 7-8, with an incli

* 356,182 lb. Troy. Trans.
† 393 feet. Trans.
I 7715 feet. Trani.
& From 13 to 19 feet. Trans.

nation of 60° to the north-east, particularly in the road from Pachuca to Real del Monte. The level is at first cut through the solid rock, (querschlagsweise) in a direction of hor. 7, towards the west ; but farther on it takes its way over three different veins, hor. 11-12, of which one alone the veta de le Soledad *, has furnished a sufficiency of silver ores to pay all the expences of the undertaking. The level was only finished in 1762, by Don Pedro Tereros, the partner of Bustamente. The former known by the title of Count de Regla, as one of the richest men of his age, had already drawn, in 1774, a net profit of more than 25 millions of livres tournoist, from the mine of Biscaina. Besides the two ships of war which he presented to King Charles the Third, one of them of 120 guns, he lent five millions of francs to the Court of Madrid, which have never yet been repaid him. He erected the great works of Regla, at an expence of 10 millions; and he purchased estates of an immense

* It is believed that this vein is the same with that which M. D'Elhuyar, began to work in the pit of Cambrera, at Moran. It appeared to me however that the veta de Cabrera, is rather the same with that of Santa Brigida, and that its principal wealth is to be found in following it towards the mine of Jesus.

+ £ 1,041,750 Sterling. Trans.
| £ 208,350 Sterling. Trans.
$£416,700 Sterling. Trans.

extent, and left a fortune to his children, which has only been equalled in Mexico, by that of the Count de la Valenciana.

The level of Moran traverses the vein of la Biscaina, in the San Ramon shaft, at a depth. of 210 metres*, below the level of the surface, on which the baritels à chevaux are placed. The profit of the proprietor has been annually diminishing since 1774. In place of cutting galleries of investigation, to discover the vein on a great extent, they continued their sinking operations to a depth of 97 metres below the level.t At that depth, the vein preserved its great wealth in sulphuret of silver, mixed with native silver, but the abundance of water increased to such a degree, that 28 baritels, each of which required more than 40 horses, were not sufficient to draw it off. In 1783, the weekly expence amounted to 45,000 francs. After the death of the old Count de Regla, the works were suspended till 1791, when they ventured to re-establish all the baritels. The expence of these machines which drew up the water, not by means of pumps, but by bags suspended by ropes, then amounted to more than 750,000 francs per annum. At length they reached

* 688 feet. Trans.
+ 317 feet. Trans.
* £ 1875 Sterling. Trans.
§ £ 31,252 Sterling. Trans.

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