C 175 3 



stances are generally dispersed through, or confusedly 

 mixed with these crystalline bodies. The veins in. 

 hard granite seldom afford much useful metal; but in 

 the veins in soft granite, and in gneis, tin, copper, and 

 lead are found. Copper and iron are the only metals 

 usually found in the veins in serpentine. Micaceous 

 schist, sienite, and granular marble, are seldom me- 

 talliferous rocks. Lead, tin, copper, iron, and many 

 other metals are found in the veins in chlorite schist. 

 Grauwacke, when it contains few fragments and exists 

 in large masses, is often a metalliferous rock. The 

 precious metals, likewise iron, lead, and antimony, are 

 found in it; and sometimes it contains veins or masses 

 of stone coaly or coal free from bitumen. Limestone 

 is the great metalliferous rock of the secondary family; 

 and lead and copper are the metals most usually found 

 in it. No metallic veins have ever been found in 

 shale, chalk, or calcareous sandstone; and they are 

 very rare in basalt and siliceous sandstone.* 



In cases where veins in rocks are exposed to the 

 atmosphere, indications of the metals they contain may 

 be often gained from their superficial appearance. 

 Whenever fluor spar is found in a vein, there is al- 

 ways strong reason to suspect that it is associated 

 with metallic substances. A brown powder at the 

 surface of a vein always indicates iron, and often tin; 

 a pale yellow powder lead; and a green colour in a 

 vein denotes the presence of copper. 



* Fig. is, will give a general idea of the apptarance ar*l arrangem.fu of rof ks 

 and veins, 



