SILVER. 



fterling. The mountain is 1 8 miles in circumference: it is 

 compofed of flate, but has a conical covering of porphyry, 

 which gives it the form of a fugar-loaf, or bafaltic hill ; it 

 rifes 697 toifes, or 480 yards, above the furrounding plain. 

 The richnefs of the veins has diminifliL-d, as they have been 

 worked to greater depths. At the furface of the earth, the 

 veins of Rica, Centeiio, and Mendifta, which traverfe primi- 

 tive flate, were filled with native filver, and filver-ores 

 throughout their whole extent. Thcfe metallic mafles rofe 

 in ridges or crefts above the furface, the fides of the vein 

 having been deitroyed either by water or by fome other 

 caufe. In I545> minerals containing from 80 to 90 marcs 

 of fiherpfr quintal were common. In the year 1574, ac- 

 cording to Acotta, the average richnefs of the ore was eight 

 or nine marcs per quintal. In 1607, the mean wealth of 

 the ores was not more than an ounce and a half to the 

 quintal. The ores are now extremely poor, and it is on 

 account of their abundance alone that the works are Hill m 

 a flourifliing Rate: for from 1574 to the year 1789, the 

 mean quantity of fdver in the ores has diminiflied in the pro- 

 portion of 170 to I ; while the abfolute quantity of filver 

 extracted from the mineb of Potofi has only dimmifhed in 

 the proportion of 4 to i. 



About fix miles from Pafco is the mountain Jauvichora : 

 it is diftinguilhed by the name of the Silver mountain. It 

 is about half a mile in diameter, and only about 30 yards in 

 depth : it is compofed of brown iron-ftone, which is inter- 

 fperfed with pure filver. This ftone does not yield more 

 than nine marcs of filver in 500 lbs. ; but there is a friable 

 white clay met with in the middle of this mals of ore, which 

 yields from 200 to 1000 marcs of filver in every 50 cwt. 

 The mountain is penetrated in all diredlions, without any 

 attention to fecurity ; fo that it is expefted it may fall in, 

 in the courfe of a few years. According to Helms, this 

 mountain yields annually 200,000 marcs of filver. 



The veins of filver at Potofi are in flate, which Hum- 

 boldt confiders as primitive : this flate is covered with a clay 

 porphyry, containing garnets. The mines of Gualgayoc, 

 in Peru, are in the Alpine lime-ftone. The veins which 

 furniih nearly all the filver exported from Vera Cruz are 

 in flate, porphyry, grauwacke, and Alpine lime-ftone : 

 the principal of thefc veins are thofe of Guanaxto, Zaca- 

 tecas, and Catoree. The vein of Guanaxto yields more 

 than one-fourth of the filver of Mexico, and a fixth part of 

 the total produce of America. This vein is, in fome parte, 

 from 147 to 150 feet in width, including the branches, and 

 has been wrought from Santa Ifabella and San Bruno to 

 Buena-Veila, a length of 42,000 feet. The moll cele- 

 brated mines in Mexico are elevated from 6000 to 9000 

 feet above the level of the fea. In the Andes, the mines 

 of Potofi, Ocuro, Pas, Pafco, and Gualgayoc, are in re- 

 gions higher than the loftiell fummits of the Pyrenees. A 

 mafs of rich filver-ore has been difcovercd near the fraall 

 town of Micuicampa, at the abfolute height of 13,450 feet. 

 The great elevation of the Mexican mines is peculiarly ad- 

 vantageous to the working of them, as the climate is tem- 

 perate, and favourable to vegetation and cultivation. 



The part of the Mexican mountains which at prefent 

 contains the greateft quantity of filver, lies beween the 

 twenty-firll and twenty-fourth degrees of latitude ; and it 

 is not a little remarkable, that the metallic wealth of Peru 

 fhould be placed at an almoft equal latitude, on the other 

 fide of the equator. In the vait extent which feparates the 

 mines of La Pas and Potofi from thofe ot Mexico, there 

 are no others which throw into circulation a great mafs of 

 the prccwus metals, but thofe of Pafco and Chota. The 



ifthmusof Panama and the mountains of Guatimala contain, 

 for a length of 600 leagues, vaft trafts of ground, in which 

 no vein has hitherto been worked with fuccefs. 



The province of Quito, and the eallern part of the king- 

 dom of New Granada, from the eighth degree of fouth 

 latitude to the feventh degree of north, are equally poor in 

 metallic wealth. It would not, however, fays Humboldt, 

 be correft to infer that thefe countries, which have been 

 convulfed and torn by volcanoes, are deftitute of the pre- 

 cious metals. Numerous metallic repofitories may be con- 

 cealed by beds of bafalt, and other rocks of fuppofed 

 volcanic origin. It fliould, however, be remarked, that 

 fome of the rocks, which Humboldt enumerates as very 

 mctalhferous, are by other geologifts confidered of volcanic 

 origin, particularly chnk-iione-porphyry, and other por- 

 phyries containing hornblende, but diltinguiftied by the ab- 

 fence of quartz and common fellpar. 



The mines of Huantajya are celebrated for the great 

 quantities of native filver they formerly produced. They 

 are fituatcd in an arid defert, and furrounded by rock-falt, 

 near the (liores of the Pacific ocean, at no great diftance 

 from the Imall port of Yquique, in the audience of Lima. 

 Thefe mines are a remarkable exception to the great eleva- 

 tion of filver-mines in Spanifh America, being placed on a 

 low and gentle declivity. Their produce is native filver, 

 vitreous filver, and horn filver; the annual amount is about 

 50,000 lbs. troy of filver, or 80,00c marcs. 



The filver-mining operations of Chili, according to Hum- 

 boldt, are in general not produdlive ; but the vein at Ufpalata 

 contains pacos fo rich, that the produce is from 2000 to 

 3000 marks in every 5000 lbs., or from 40 to 60 marc* 

 per quintal. Molina, in his Hiitory of Chili, dcfcribes the 

 vein at Ufpalata, on the Andes, as being nine feet in thick- 

 nefs. It has been traced 90 miles, and is fuppofed to extend 

 300 miles. From the main vein there are branches on each 

 lide, which extend to the neighbouring mountains : fome 

 of thefe branches are 30 miles in length. This is the largeil 

 metallic vein which is at prefent known in the world. 



According to Humboldt, the greateft part of the filver 

 extracted from the bowels of the earth in Peru is furniftied 

 by a fpecies of ore called the pacos, of an earthy appearance, 

 which M. Klaproth analyfcd, and was found to confift of 

 almoft imperceptible particles of native filver with the 

 brown oxyd of iron. In Mexico, on the contrary, the 

 greateft quantity of filver annually brought into circulation 

 is derived from vitreous filver-ore, grey filver-ore, horn-ore, 

 and black and red filver-ores. Native filver is not extracted 

 in fufficient quantity to form any confiderable proportion 

 of the total produce of the mines of New Spain. It is, 

 fays this traveller, a very common prejudice in Europe, 

 that great mafles of native filver are very common in the 

 mines of Mexico and Peru, and that in general the mines 

 of mineralized filver, deftined to amalgamation, or to fmelt- 

 ing, contain more ounces, or marcs of filver, to the quintal, 

 than the filver-ores of Saxony or Hungary ; but he adds, 

 I was furprifed to find that the number of poor mines 

 greatly exceeds thofe of the mines which, in Europe, would 

 be efteemed rich. It is at firft difficult to conceive how the 

 famous mine of Valenciana, in Mexico, can regularly fupply 

 30,000 marcs of filver per month, as the vein confifts of 

 fulphuretted filver, difl'eminatcd in almoit imperceptible 

 particles through the matrix. In the formation of thefe 

 veins, it (hould appear that the diftribution of filver has 

 been very unequal, being fometimes concentrated at one 

 point, and at other times dilleminated in the vein through 

 the matrix or gangue ; for, in the midft of the pooreft ore? 



are 



