232 Mexican Mines. 



contain beds of porphj'iy, ■svhicli, 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 ap- 

 pears clayey, and sometimes analogous to splintery hornstone. 

 The presence of hornblende is frequently announced, merely 

 by greenish stains intermingled with common and vitreous 

 feldspar. At very great elevations, for example in the beau- 

 tiful forest of oak and pine of Oyamel, we find porphyries 

 with a base of pearl-stone, containing obsidian in layers and 

 nodules. 



" What I'elation exists between these last beds, which several 

 distinguished mineralogists consider as volcanic pi-oductions, 

 and the porphyries of Pachuca, Real del Monte, and Moran, 

 in which nature has deposited enormous masses 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 vitreous feldspar. 



" The district of mines of Real del Monte does not display — 

 as at Freiberg in Saxony, Derbyshire in England, or as in the 

 mountauis 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 Schem- 

 nitz, in Europe, or those of Guanaxuato and Potosi in Ame- 

 rica, of which the riches are contained in a few mineral de- 

 positions 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 tra- 

 verse or derange them. 



" The veta de la Biscaina, of less considerable dimensions, 

 but perhaps still richer than the vein of Guanaxuato, was 

 successfully 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 333,969 ounces of 

 silver. The great quantity of water which filti'ated through 

 the crevices of the porphyritic rock, joined to the imperfection 

 of the means of drawing it off, compelled the miners to aban- 

 don the works when they were yet only 65 fathoms in depth. 

 A very enterprising individual, 13on Joseph Alexandre Busta- 

 mente, was courageous enough to undertake a level near 

 Moran; but he died before completing this great work, which 



is 



