42 



clay-slate formation ; also lead and iron pyrites, disseminated in 

 porphyritic rocks in the same locality. 



Gold is principally found as a superficial efflorescence on the 

 face of rocks and in cavities, seldom or never in a close grain or 

 compact rock. It is found in the Brazils, Chili and New Gra- 

 nada, in the tender part of porphyry and clay-slate. It is the 

 destruction or waste of these friable rocks that produces the rich 

 alluvial soil of America. 



The porphyry of Cornwall contains nests of yellow copper ore 

 varying from a few ounces to several tons' weight. In North 

 Wales and Cumberland similar metalliferous rocks are common ; 

 they are also very abundant in Ireland. 



Moss copper is well known to miners : it is the produce of a 

 metalliferous rock, out of which it vegetates like common moss. 

 Gold, silver, pyrites, lead, and indeed all metals, may be seen 

 occasionally growing out of rocks where the situation and cir- 

 cumstances are favourable for their formation. 



The minerals are found in the rocks in solution as common as 

 in the solid, indeed it is the state in which we consider them to 

 be previous to their crystallization. All rocks are more or less 

 impregnated with mineral solvents. The cupreous springs are 

 very abundant in Chili, Peru, New Granada, Cuba and New 

 Brunswick : they are to be seen also in Ireland, Anglesea, Spain 

 and Hungary. The copper in solution is obtained by precipi- 

 tating it by means of iron. The bog-iron ore is of similar origin, 

 and is formed precisely in the same manner as the calcareous 

 and siliceous tuffa. 





