8. Silver is found, particularly in veins and beds, in primitive and transition for mations; though some veins of this me tal occur in secondary strata. The rocks richest in it are gneiss, mica-slate, clay slate, greywacke, and old alpine limestone. Localities of silver-ore itself are not nu merous, among secondary formations ; but it occurs in combination with the ores of copper or of lead.
4. Copper exists in the three mineral epoehas : 1. In primitive rocks, princi pally in the state of pyritous copper, in beds, in masses, or in veins ; 2. In tran sition districts,. sometimes in masses, sometimes in veins of copper pyrites ; 3. In secondary strata, especially in beds of cupreous schist.
5. Lead occurs also in each of the three mineral epochas ; abounding particularly in primitive and transition grounds, where it usually constitutes veins, and occasionally beds of sulphuretted lead (galena.) The same ore is found in strata or in veins among secondary rocks, asso ciated now and then with ochreous iron oxide and calamine (carbonate of zinc ;) and it is sometimes disseminated in grains through more recent strata.
6. Iron is met with in four different mineral eras, but in different ores. Among primitive rocks magnetic iron ore and specular iron ore occur chiefly in beds, sometimes of enormous size : the ores of red or brown oxide of iron (hae matite) are found generally in veins, or occasionally in masses with sparry iron, both in primitive and transition rocks ; as also sometimes in secondary strata ; but more frequently in the coal-measure strata, as beds of clay-ironstone, of glo bular iron oxide, and carbonate of iron. In alluvial districts, we find ores of clay ironstone, granular iron-ore, bog-ore, swamp-ore, and meadow-ore. The iron ores which belong to the primitive period have almost always the metallic aspect, with a richness amounting even to 80 per cent. of iron, while the ores in the poste rior formations become, in general, more and more earthy, down to those in allu vial soils, some of which present the ap pearance of a common stone, and afford not more than 20 per cent. of metal, though its quality is often excellent.
7. Mercury, as a sulphuret, occurs prin cipally among secondary strata in dissem inated masses, along with combustible substances ; though the metal is met with occasionally in primitive countries.
8. Cobalt belongs to the three mineral epochas ; its most abundant deposits are veins in primitive rocks ; small veins con taining this metal are found, however, in secondary strata.
9. Antimony occurs in veins or beds among primitive and transition rocks.
10. Bismuth and nickel do not appear to constitute the predominating substance of any mineral deposits ; but they often accompany cobalt.
11. Zinc occurs in the three several for mations; namely, as sulphuret, or blend°, particularly in primitive and transition rocks ; as calamine, in secondary strata, usually along with oxide of iron, and sometimes with sulphuret of lead.
In the analysis of ores, it is impossible to lay down any general rule, so numer ous are the ores themselves, and so di versified the means necessary to be adopt ed in the various analytic processes. Un der each particular metal will be found an account of its most important ores, and we shall here restrict ourselves to a few general remarks on the theory of smelting ores.
It is probable that the coaly matter em ployed in that process is not the immedi ate agent of their reduction ; but the char coal seems first of all to be transformed by the atmospherical oxygen into the ox ide of carbon, which gaseous product then surrounds and penetrates the interior sub stance of the oxides, with the effect of de _them, and carrying off their oxygen. That this is the true mode of
action, is evident from the well-known facts that bars of iron, stratified with pounded charcoal, in the steel-cementa tion chest, most readily absorb the car bonaceous principle to their innermost centre, while their surfaces get blistered by the expansion of carburetted gases formed within ; and that an intermixture of ores and charcoal is not always neces sary to reduction, but merely an inter stratification of the two, without intimate contact of the particles. In this case, the carbonic acid which is generated at the lower surfaces of contact of the strata, rising up through the first bed of ignited charcoal, becomes converted into carbonic oxide ; and this gaseous matter, passing up through the next layer of ore, seizes its oxygen, reduces it to metal, and is it self thereby transformed once more into carbonic acid ; and so on in continual al ternation. It may be laid down, however, as a general rule, that the reduction is the more rapid and complete the more inti mate the mixture of the charcoal and the metallic oxide has been, because the for mation of both the carbonic acid and car bonic oxide becomes thereby more easy and direct. Indeed the cementation of iron bars into steel will not succeed, un less the charcoal be so porous as to con tain, interspersed, enough of air to favor the commencement of its conversion into the gaseous oxide ; thus acting like a fer ment in brewing. Hence, also, finely pulverized charcoal does not answer well, unless a quantity of ground iron cinder or oxide of manganese be blended with it, to afford enough of oxygen to begin the generation of carbonic oxide gas ; where by the successive transformations into acid and oxide are put in train.
Iron is the most abundant of ores our country affords. Its value is ten times that of gold and silver, and one half the value of all the metals produced in the United States. Iron is found in every State of the Union.
The most valuable mine is one in Salis bury, Ct., which yields 3,000 tons annu ally. The mines in Duchess and Colum bia counties, in the State of New-York, produce 20,000 tons of ore ; Essex county, 1,500 tons ; Clinton, 8,000; Franklin, 600; St. Lawrence, 2,000; amounting in all to more than $500,000. The value of the iron produced in the United States, in 1835, was $5,000,000 ; in 1837, $7,700,000. In Ohio, 1,200 square miles are under laid with iron. A. region explored in 1838 would furnish iron sixty-one miles long., and six miles wide ; a square would yield 3,000,000 tons of pig-iron ; so that this district would contain 1,000,000,000 tons. By taking from this region 400,000 tons annually, (a larger quantity than England produced previous to 1829,) it would last 2,700 years—as long a distance, certainly, as any man looks ahead 1 In the States of Kentucky and Tennessee, 100,000 tons are annually manufactured.
The most extensive lead mines in the world are in Missouri, where the lead re gion is seventy miles long by fifty wide. These mines in 1826, produced 7,500,000 tons, and the whole produce of the United States was 8,322,105.
The quantity of lead manufactured in the United States, in 1828, was 12,811,730 lbs. ; in 1820, 14,541,310 lbs. ; in 1838, 8,332,105; and in 1842, 4,281,687.
The copper trade, until within a year or two, has not been of much importance, as the results of the efforts made were not such as to justify any great opera tions. But now it appears to be attract ing a good deal of attention. Whether the demand of the copper stock is a fair index to the value of the copper regions remains to be seen.