634 



GEOLOGY. 



in several of the Cornish mines ; while mines in the south of France have conducted 

 first to iron, next to silver, and lastly to copper. The metallic veins are chiefly 

 found in rocks of the primary and transition series, none being worked in Great Britain 

 above the new red sandstone, nor any of much importance above the carboniferous 

 limestone. That variety of iron ore, however, called by mineralogists haematite, from 

 the Greek word signifying " blood," and also termed blood-stone, occurs in the lias 

 and chalk of the Pyrenees ; and in the Andes of Chili, the tertiary strata, which have 

 become metamorphic by proximity to granite, are traversed by true metallic veins of 

 iron, copper, arsenic, silver, and gold, which proceed from the underlying granite. The 

 great deposits of copper are found in the older sedimentary and the unstratified rocks, 

 of which the county of Cornwall is composed, which produces more of this metal than 

 all the other European mines collectively. Scarcely an example occurs in which a vein 

 has been cut out, or its termination been reached ; for when abandoned, it is generally 

 owing to its having become poor, or to the expense of going deeper being greater 

 than what the probable produce would yield. So extensively are some of the mining 

 operations for copper carried on, that in the Consolidated Mines of the parish of Gwennap, 

 near Redruth, the engine-power employed, if exerted to its full extent, is equal to 

 the work of from seven to eight thousand horses. Lead is found most abundantly in 

 the carboniferous limestone, in considerable quantity also in the lower stratified rocks, 

 likewise in granite and in the coal measures, but not in any of the strata above the coal. 

 The veins in the limestone are the largest and the richest in ore ; and the same vein 



which in a limestone stratum may have a 

 width of seventeen feet, has been found to 

 contract to three in the sandstone below. 

 Silver is met with chiefly in primary 

 strata, and also in unstratified rocks. The 

 rich mine of Potosi in South America, dis 

 covered in 1545, which yielded in the space 

 of eighty-three years from its discovery 

 four hundred millions of ounces, is situated 

 in primary slate. 



Besides occurring in veins, silver has 

 been found in large insulated masses, as in 

 one of the Peruvian mines, in which a lump 

 was discovered weighing eight hundred 

 pounds. At Konigsberg, in Norway. 

 a mass of upwards of five hundred 

 pounds' weight was found ; and masses of 

 a hundred pounds have frequently been 

 yielded by the mines of Freiberg in 

 Saxony. Gold also occurs in veins in the 

 older sedimentary strata, the gneiss and 

 mica-slate in Mexico, as well as in the 

 unstratified rocks. It has been found in 

 masses likewise, varying from eighteen to 

 forty-five pounds' weight, in the Ural 

 mountains, in Columbia, and in Peru. 

 The subject of the occurrence of the metals 



interior ot a silver Mine. in veins and masses is most obscure ; but 



the general fact, that they are most abundantly situated near the junction of stratified 



