300 MINERALOGY. 



of these proportions is a most important step towards 

 the advancement of mineralogy to the dignity of a 

 demonstrative science. 



Metallic Feins. 



The veins which afford metallic substances are 

 fissures more or less vertical, filled with a material 

 different from the rock in which they exist, and 

 generally extending in an east and west direction. 



A brown powder at the surface of a vein always 

 indicates iron, and often, also, tin ; a pale yellow 

 powder, lead ; and a green colour in a vein, or in 

 water, denotes the presence of copper. 



Silver is known to be found in association with cer- 

 tain limestones only, and where these cease it will be 

 sought for in vain. 



Dolcoath Mine. 



Dolcoath mine, in Cornwall, is 456 yards deep, 

 and is still very productive. 



Gold. 



The total quantity of gold produced annually 

 throughout the world has been estimated at 1,240,000 

 ounces, but it appears too large an estimate, consider- 

 ing how unproductive the South American mines have 

 become within the last 30 years. 



In procuring the pure metal the rough ores of gold 

 are first broken in the stamping mill and washed, by 

 which the lighter and earthy parts are separated. 

 They are then submitted to the action of mercury, 

 which dissolves the gold, and a process of distillation 

 afterwards separates the amalgam, and the gold is 

 produced in a state of comparative purity. 



Solid and ponderous as gold appears to be, Sir 

 Isaac Newton supposes the pores or interstices be- 



