372 Mr. J. Taylor's Lectures on Metallurgy. 



Primitive rocks: — Granite; gneiss; mica slate; clay slate. 



Secondarij rocks: — Gritstone or sandstone ; limestone; shale 

 or plate. 



Geologists indeed enumerate many others, but miners con- 

 sider them as modifications of the same. 



In this country clay slate is the most productive of the pri- 

 mitive class, and limestone of the secondary. 



The metallic ores are found occupying certain spaces in 

 these rocks, which have been arranged under the names of 

 veins, beds, and masses. The two first are the most usual. 



Mineral veins, and the particulars of their position, direction, 

 and appearance, have been formerly described. They are ta 

 be understood as fissures which have been filled up by dif- 

 ferent mineral substances. . Professor Brande very justly re- 

 marked that the term Vein was objectionable, as it conveys 

 the idea of a tube or pipe filled with metal, whereas it is a 

 plate or lamina. They extend in nearly right lines, are of 

 unequal thickness, penetrate to unknown depths, and usually 

 are somewhat inclined fi*om the perpendicular. They contain 

 a gi-eat variety of metals differing in different countries, and 

 in distinct veins in the same country. 



English miners have different terms for veins : in Cornwall 

 they are called Lodes ; in Derbyshire, Rakes ; and the term 

 Dyke sometimes used describes the same thing. 



In these deposits the ores are accompanied by earthy sub- 

 stances generally in a crystallized or sparry form called Vein- 

 stones, Matrix, Gangue. 



Beds are the other kind of regular depositoiy of metallic 

 ores. These are flat or tabular masses interposed between 

 strata of rock, and thus resemble beds of coal. They are 

 seldom very thick, and mostly produce iron, manganese, and 

 sometimes lead. 



Masses, or as they are sometimes called Pipes, are irregular 

 deposits of the metals, and, not being usual, need not occupy 

 much of our notice. 



^ The metals or their ores are also liometimes found in allu- 

 vium, such as gravel and sand m valleys, and particularly gold 

 in a native form in many places, and tin ore in Cornwall and 

 Banca. 



Mr. Taylor proceeded to enumerate and exhibit specimens 

 of the metals in all their principal varieties. 



As the metals are generally intimately mixed and blended 

 w ith earthy matter or spar, or often with other metallic matter 

 of inferior value ; before the processes of smelting or reduction 

 by fire are resorted to, various mechanical operations are used 

 to free thein from such admixtures as nuich as possible, so 



tliat 



