8 THE WONDERS OF GEOLOGY. 



the ground, and have therefore been (perhaps for ages) subjected to 

 those atmospherical agencies, which the finished edifice must, in its 

 turn, encounter. 



Metals. — The researches for metals have ever interested mankind 

 in a high degree, and on no subject are they more liable to error and 

 imposition. Happily, the most important metal, iron, is the most 

 abundant. But iron ores are not always known by the uninstructed; 

 some of the most valuable are not attracted by the magnet, until 

 they have been heated in contact with carbon or hydrogen. Other 

 ores are so completely disguised, that they are not recognised at all 

 by those acquainted with the purified metals alone. This arises 

 from their combination with various substances, chiefly oxygen, 

 sulphur, acids, or arsenic, which, on account of the great change 

 they produce in the properties of metals, are called mineralizers. 

 Iron pyrites, an abundant mineral of little value, is frequently 

 mistaken for gold, because it is usually yellow; and this, notwith- 

 standing it is hard and brittle, while gold is soft and malleable, so 

 that a mere blow of a hammer would detect the difference. Yellow 

 mica has been gathered for gold dust ; and silvery mica, and white 

 arsenical iron, have been mistaken for silver. 



Calamine, the native oxide of zinc, has no resemblance to any metal 

 whatever; and tin-stone, the native oxide of tin, has none to that 

 metal ; and both would be rejected by an ignorant observer. The same 

 may be said of the sulphuret of silver, the gray sulphuret of copper, 

 the chromate, molybdate, carbonate, phosphate, and sulphates of 

 lead, and many more. Few persons, indeed, trust themselves to 

 carry on great works in mining, without previously consulting pro- 

 fessional men; some are, however, so perverse, or blinded, as to 

 persist even against the best counsels, and they, of course, pay 

 the penalty of their folly in disappointment, and oftentimes in 

 utter ruin. 



Geological associations of metals. — It is well known to geologists, 

 that metallic veins are rarely found in the most recent formations ; 

 and, with the exception of iron, and of alluvial deposits of other 

 metals, they seldom occur in great abundance, until, in the descend- 

 ing series, we approach or pass the geological epoch of coal. In the 

 transition rocks, certain metals abound, while others occur in the 

 primary, and there is no rock so old that it may not contain some 

 of the metals. Sound scientific views of the geological structure of 

 a country, will therefore serve as an important guide in the research 



