Dr. Mac CuUoch on Miiieral Veins. l93 



it remains to be seen, by a further extension of rational and 

 unbiassed investigations, whether they are not swallowed up by 

 amass of exceptions. It is said, for example, that in a vein 

 near Callington in Cornwall, passing through schist and gra- 

 nite, the copper which it contains is found in the former, and 

 the tin in the latter, part. It is further said, that in Cornwall, 

 similar veins are poor in the schist, and rich in the granite. 

 It is also asserted, that vei.is are most productive at the junc- 

 tion of the schist and granite, not only in Cornwall, but in 

 Silesia and elsewhere. There is not one example of this nature, 

 to which there are not exceptions many times exceeding them, 

 for which the reports of the same observers may be consulted. 

 It would be endless to quote instances; as it would be fruitless 

 here to record all the observations that have been made on 

 these subjects ; since the conclusion would be, to draw, as might 

 equally be done without them, no conclusions. Whether, on 

 the subject of the influence which strata have over the contents 

 of veins, any exception ought to be made in favour of Derby- 

 shire, where this is said to occur, it seems fruitless to ask ; 

 until miners shall fairly enter on the field of accurate observa- 

 tion, or geologists, discarding their prejudices, shall seriously 

 turn their attention to a branch of the science which is, most 

 particularly, its opprobrium. 



Of the Theory of Mineral Veins. 

 On such a foundation, it has been attempted to build theories 

 of mineral veins ; and, as is usual in similar cases, the opposing 

 opinions have. been maintained with a vehemence proportioned 

 to the want of evidence on both sides. It is necessary to state 

 these two hypotheses, before inquiring into the circumstances 

 by which either of them may be countenanced or opposed ; 

 and it is scarcely necessary to say, that the only important 

 question at issue, concerns the manner in which the Contents of 

 the veins were formed and introduced ; as the fissures in which 

 these are contained have formerly come under review. 



It is said, on one hand, that all the materials of veins have 

 been deposited from the same universal solution whence the 

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