A trum, of which the inclination is 65°, separates from the inferior branch, (cuerpo baxo) and cuts the folia of the rock of the wall. This phenomenon, and the great number of druses, abounding with amethyst crystals, I found in the mines of Rayas, which affect the most different directions, are sufficient to prove that the veta madre is a vein, and not a bed. Other proofs not less convincing might be drawn from the existence of a vein, (veta del caliche) wrought in the compact lime-stone of Animas, which is parallel to the principal vein of Guanaxuato, and has exhibited the same silver ores. Is this identity of forma tion, ever found between two metalliferous beds, which belong to rocks of very different antiquity? The small ravins into which the valley of Marfil is divided, appear to have a decided influence on the richness of the veta madre of Guanaxuato, which has yielded the most metal where the direction of ravins, and the slope of the mountains, (flaqueza del Cerro) have been parallel to the direction and inclination of the vein. When we stand on the elevation of Mellado, near the shaft which was sunk in 1558, we observe that the veta madre is in general most abundant in ores towards the north-west, towards the mines of Cata and Valenciana ; and that to the south-east towards Rayas and Santa Anita, the produce has been at once richer, rarer, and more inconstant. Besides in this celebrated vein, there is a certain middle region which may be considered as a depository of great riches; for above and below this region, the ores have yielded an inconsiderable share of silver. At Valenciana the rich ores have been in the greatest abundance, between 100 and 340 metres in depth below the mouth of the gallery. This abundance appeared at Rayas at the surface of the earth; but the gallery of Valenciana is pierced according to my measurements †, in a plain which is more than 156 metres above the level (galerie d'ecoulement) of Rayas; which might lead us to believe that the depository of the great wealth of Guanaxuato is found in this part of the vein, between 2130 and 1890 metres of absolute height above the level of the ocean: § The deepest works of the mine of Rayas, (los planes) have never yet reached the inferior limit of this middle region; while the bottom (das tiefste) of the mine of Valenciana, the gallery of San Bernardo has unfortunately passed this limit more than 70 metres. Hence * Between 328 and 1115 feet. Trans. † See my Recueil d'Observations Astronomiques, Vol. i. p. 324. No. 332-357. the mine of Rayas continues to furnish extremely rich ores, while at Valenciana they have endeavoured for some years to supply by the extraction of a greater quantity of ores the deficiency in their intrinsic value. The mineral substances which constitute the mass of the vein of Guanaxuato, are common quartz, amethyst, carbonate of lime, pearl spar, splintery hornstone, sulphuret of silver, dendritic native silver, prismatic black silver, deep red silver, native gold, argentiferous galena, brown blende, spar iron, and copper and iron pyrites. We observe besides though much more rarely, crystallized feldspar (the rhomboidal quartz of the Mexican mineralogists) calcedony, small masses of spar-fluor, capillary quartz (haarformiger quartz), grey copper ore (fahlerz) and columnar carbonate of lead. The absence of the sulphate of barytes and muriate of silver, distinguishes the formation of the vein of Guanaxuato from that of Sombrerete, Catorce, Fresnillo, and Zacatecas. Those mineralogists who are interested in the study of regular forms, find a great variety of crystals in the mines of Guanaxuato, and especially in the red and black sulphuret of silver, and in the calcareous spar, and the brown spar.* *On the pearl spar of Guanaxuato, see Klaproth's Beiträge, B. iv. p. 128. This variety of brown-spar (braun-spath) exhibits microscopic crystals imbricated and collected in very The abundance of waters which filtrate through the crevices of the rock and the gangue, vary very much in the different points of the vein. The mines of Animas and Valenciana are entirely dry, though the works of the latter occupy a horizontal extent of 1500, and a perpendicular depth of 500 metres.* Between these two mines, in which the miner is incommoded by the dust and extreme heat †, lie the mines of Cata and Tepeyac, which remain inundated, because they do not possess sufficient mechanical force to draw off the water. At Rayas, it is drawn off in a very expensive manner by means of baritels a mulets, placed in the interior of the traverses, and raising the water not by pumps, but by the action of chapelets de caissons of a very imperfect construc tion. One is astonished to see mines of such considerable wealth without any level ‡, while the neighbouring ravins of Cata and Marfil, and thin prisms. The interlacing of these prisms, (parillas) is so regular that they constantly form equilateral triangles. * 4920 aud 1640 feet. Trans. + From 22° to 27° centigrade, (71° and 80°. Fahr. Trans.); the temperature of the exterior air being 17° (62° Fahr.) In the district of the mines of Freiberg, which however do not yield annually the seventh part of the money extracted from the single mine of Valenciana, they have executed two levels, of which the one is 63,213 metres, and the other 57,310 metres in length (207,390 and 188,023 feet. Trans.) the plains of Tenascatio, which are lower than the bottom of Valenciana, appear to invite the miners to undertake works which would both serve to draw off the water, and to transport the ores to the place where they are smelted and amalgamated. The Valenciana is almost the sole example of a mine, which for forty years has never yielded less to its proprietors than from two to three million of francs of annual profit. It appears that the part of the vein extending from Tepeyac to the North-west, had not been much wrought towards the end of the 16th century. From that period the whole tract remained forsaken till 1760, when a Spaniard who went over very young to America, began to work this vein in one of the points which had till that time been believed destitute of metals (emborascado). M. Obregon + (the name of this Spaniard) was without fortune; but as he had the reputation of being a worthy man, he found friends who from time to time advanced him small sums to carry on his operations. In 1766, the works were already 89 metres in depth ‡, and yet the expences greatly surpassed the value of the metallic produce. With a passion for mining * From 82,506l. to 123,7591. per annum. Trans. |