VEIN. 



than 14,000 feet above the level of the fea, that the pro- 

 digious mafs of mercurial ores is found at Guauca Velica, 

 where, in the fpace of two centuries, more than 15,000 

 quintals of this metal have been procured. 



But the fafts moft oppofed to the theory of Werner are 

 thofe \Yhich we have ftated, namely, that when a metallic 

 vein pafles through different ftrata, the mineral fubftances it 

 contains generally vary in each ftratum, either in kind or 

 quality. Sometimes an entire change takes place, as from 

 tin to copper or lead ; in other inflances, the vein will con- 

 tain the fame kind of ore in the different ftrata, but it will 

 be invariably richer or poorer in fome of the ftrata than in 

 others, and there will be certain ftrata in which fcarcely any 

 ore occurs. Very freqOently where the fame kind of me- 

 tallic matter is contained in the vein, it will be mineralized 

 or combined with different fubftances, as the vein pafles 

 through different beds : thus we find a metallic fulphuret 

 more prevalent in one part, and a metallic fait or oxyd in 

 another part of the vein. 



In Derbyfhire, where the veins of lead pafs through dif- 

 ferent beds of mountain lime-ftone, which alternates with 

 beds of bafaltic amygdaloid, provincially called toad-ftone, 

 it is found that the vein fcarcely ever contains lead as it 

 paffes through the toad-ftone, where it is always much nar- 

 rower, and in fome places appears to be entirely cut off by it ; 

 but on finking into the under beds of lime-ftone, the vein is 

 found again, and is as produftive as in the upper beds. 

 Where the vein can be traced through the toad-ftone, it 

 contains calcareous fpar, and fometimes a few particles of 

 lead-ore. If veins had been filled from above by metallic 

 folutions, it is impoffible to conceive that the nature of the 

 rock could change the quality of the ore ; much lefs could 

 the ore difappear in one ftratum, and appear again in a 

 ftratum below it. ProfefTor Jamefon, in a paper published 

 in the Memoirs of the Wernerian Society, has attempted to 

 explain the difficulty prefented by the interruption of the 

 veins in Derbyfliire, on the fuppofition that the different 

 beds of fime-ftone and toad-ftone, together with the metallic 

 veins, were contemporaneous, and that the toad-ftone cut 

 through the veins at the period of their formation. On this 

 hypothefis, Mr. Bakewell, in his Introduftion to Geology, 

 remarks ; " The exiftence of different organic remains in 

 the tipper and lower beds of the mountain lime-ftone in 

 Derbyfhire, precludes the poffibility of thefe beds having 

 been all formed at the fame time. The zoophytes in the 

 lower beds of rock could not be living and co-ex iftent with 

 the fhell-fifh in the upper, nor with the vegetables, the re- 

 mains of which are occafionally found in the fand-ftone that 

 covers the whole, and into which the veins fometimes fhoot. 

 Cuvier has well obferved, that the exiftence of different or- 

 ganic remains in the upper and lower ftrata offers incon- 

 teftible proofs that they were formed in fuccelfion over each 

 other." In point of faft alfo, the veins are not always 

 cut off by the toad-ftone ; but they are never produftive 

 of ore, where they pafs through it, except in very fmall 

 particles. 



Thefe fafts are not lefs oppofed to the igneous theory of 

 metallic veins than to that of Werner. If metallic veins 

 had been filled with their contents by the operation of fub- 

 terranean fire, which cracked the furface, and injefted the 

 metallic matter in a ftate of fufion, it is impoffible to con- 

 ceive that the nature of the rock, through which the veins 

 pafs, could have produced any material change in the quality 

 of the ore. MetalHc ores may, in fome inftances, have 

 been formed flovvly by exhalations from fubterranean fires ■, 

 as fpecular iron-ore, and even gold, has been found in the 

 craters of volcanoes ; and the phenomena, prefented by the 



lava which deftroyed Torre del Grecco in 1794, indicate 

 the manner in which fuch ores are formed. The lava had 

 buried entire houfes for more than twelve months, at the 

 latter end of which time it had confiderably cooled ; and 

 when the houfes were opened, pieces of iron were found 

 converted into a ftate of black, red, and magnetic oxyds, 

 having the hollow parts and interftices filled with a brownifh- 

 red tranfparent oxyd of iron, and with fpecular iron-ore. 

 In the articles made of iron, which had undergone this 

 change, the external form was fcarcely altered, which 

 evinces that the cryftals had been produced by fublimation. 

 Copper articles were changed into cryftallized red oxyd of 

 copper, and red oxyd with green and blue carbonate. 

 From the abfence of metallic fulphurets, it is inferred that 

 the lava contained little, if any, fulphur. Thefe changes 

 Ihew that metallic matter may be fublimed and converted 

 into the ftate of ore by fubterranean heat, at a much lower 

 degree of temperature than has been fuppofed.. 



There is a circumftance on which thofe who contend for 

 the aqueous formation of metallic veins have laid much , 

 ftrefs. In fome inftances, rounded pieces of ftone, appa^ 

 rently refembling water-worn pebbles, have been found in 

 mines at a confiderable depth ; but as many veins contain 

 hollow fpaces, through which water is continually running',! 

 the formation of pebbles might admit of a fatisfaftory ex* 

 planation, without fuppofing that thefe pebbles had fallen in 

 from above. The pebbles which we have feen of this kindj 

 from the mines in Cornwall, are all of a chlorite fchiftusJ 

 and the form oblate, prefenting the appearance which mayl 

 frequently be obferved in rocks of the fame kind. It is inl 

 all probability an original formation, and not a breccia from,1 

 pre-exifting rocks. 



There is another circumftance which appears to haveJ 

 efcaped the attention of geologifts. The water in the mines 

 of Cornwall, particularly in the vicinity of copper veins,! 

 has a temperature confiderably above that of the natura 

 temperature of the earth : it is faid to be at 70° Fahrenheit ; 

 and the working miners, from its fenfible warmth, can preJ 

 dift with certainty the vicinity of a copper vein. The in- 

 creafe of temperature, if any, ia the vicinity of tin veins is^ 

 lefs fenfible. 



From hence, as well as from various appearances in mines, 

 we are led to infer that there are certain chemical changes 

 now going on in the interior of the earth ; and it is from a 

 more enlarged acquaintance with thefe phenomena, that we 

 can alone expeft to obtain a fatisfaftory theory of the form- 

 ation of metallic veins. 



The following is a fummary account of the rocks and 

 fituations in which metallic ores are generally found. 



Platina, and the recently difcovered metals, palladium^ 

 rhodium, ofmium, and iridium, have not been hitherto 

 found in veins, but in the fands of rivers. The four latter 

 metals are found as alloys in the grains of platina. See 

 Platina, Palladium, &c. 



Gold and filvcr are found in veins, and diffeminated in 

 primary and tranfition rocks, in porphyry, fienite, and the 

 lower fand-ftone. Gold has been occafionally difcovered in. 

 coal, and is very abundantly diffeminated in the fands of 

 fome rivers. See Gold and Silver. 



Mercury is found in flate, in lime-ftone, and in fecondary 

 ftrata. See Mkrcury. 



Copper occurs in veins and beds in primary and tranfition 

 rocks, in porphyiy and fienite, and occafionally in fand- 

 ftone. Maffes of native copper, of large fize, are found on 

 the furface of the ground, in the interior of North America. 

 See Copper. 



Lead and zinc octur in veins, and diffeminated in primary 



and 



