Chap. 1 8.] Mines. ii<j 



of the mine ; the other which covers it, is called the 

 roof. Sometimes, however, the metallic ftrata, which 

 are always more irregular than the other ftrata of which 

 the. mountain is compofed, interfect the bodies which 

 furround them in a variety of directions. The metal- 

 lic ores are accompanied with ftony matters, which 

 feem to have been formed at the fame time. Thefe 

 ftone are ufually quartz and fpar; they are called the 

 rider or matrix * of the metal, and muft neither be con- 

 founded with the mineralizing fubftance which is inti- 

 mately combined with the metal, nor with the general 

 mafs of ftone, of which the mountain containing the 

 metal is compofed. It is obferved that the vegetables 

 which grow on metalliferous mountains are dry, the 

 trees fmall, fmuous, and deformed, and the fands often 

 exhibit metallic colours. Mineral metallic fprings 

 are ufually found in the vicinity ; by the examination 

 of which, and of the fands over which they flow, & 

 tolerably accurate judgment may be formed of the 

 metallic contents of the neighbouring ftra':: 1 . When 

 metallic veins appear at the furface of the earth, the 

 ground may be broken into with great probability of 

 advantage, and the boring inftrument, by bringing up 

 the jubilances which compofe the internal parts of the 

 mountain, together with the metallic minerals, ferves 

 to fhew their quality, as well as the reflftance which 

 may be expected in digging. 



Before a metallic vein is wrought with a view to 

 profit, it is neceiiary to afccrtain the proportion of 

 metal contained in it, and this is called aftaying. In 

 thefe fmall trials the fusibility of the mafs is inereafed 

 by the addition of three times the quantity of the black 

 flux, which is made by burning together two parts of 



* So called from its frequently inclofiug the ore. The fparry 

 matters are alio {bmetimes called by ir.ineralogifts gangues. 



I 2 tartar 



