184 Dr. Mac Culloch on Mineral Veins. 



they are to be expected, what courses they hold, what various 

 forms and accidents they may display, nor what substances they 

 contain. Where little information can be procured, much will 

 not be expected. 



Although mineral veins may exist without necessarily con- 

 taining metallic substances ; yet, as the general characters of 

 these are the same, they do not require to be distinguished 

 here, farther than as may relate to the nature of their contents. 

 Minerals of many kinds are also occasionally found in reposi- 

 tories which cannot properly be called veins, and metallic sub- 

 stances are not even limited to these. To describe these latter 

 cases first, will be to clear the present inquiry of circumstances 

 which would otherwise encumber it. 



Many metallic minerals are found scattered among the con- 

 stituents of the compound rocks, so as almost to form parts of 

 their composition. Thus, oxydulous iron is found in granite, 

 gneiss, sandstone, and trap ; molybdena in gneiss ; and iron 

 pyrites in slate, shale, and limestone. They sometimes, also, 

 occur independently ; neither forming part of the composition 

 of rocks, nor included in distinct repositories. In this way, 

 pyrites is found in innumerable situations ; copper in the trap 

 rocks ; and oxydulous iron in the products of volcanic fire. 

 Lastly, some of these are found accumulated in such quantities 

 in particular spots, still without forming veins, as to admit of 

 being wrought for economical purposes. Cobalt thus occurs 

 in sandstone, as does copper. Iron, in the form of ironstone 

 and bog-ore, is known to abound in beds ; the first among the 

 coal strata, and the latter in alluvial soils. Thus, also, tin 

 and gold are found among alluvial soils ; but, in these cases, 

 the origin of the metals is, without difficulty, inferred to be in 

 distant veins. It is likewise understood, that manganese oc- 

 curs in the form of beds ; as has also been said to happen with 

 respect to mercury, copper, lead, and silver ; but it is neces- 

 sary to remember, that veins, holding a course parallel to the 

 including strata, have sometimes been mistaken for beds. 



Such parallel veins are, however, sometimes distinguished 

 by the term oi flat, while the intersecting ones are called rake 



