REPORT ON AIINERAL VEINS. 19 



out by these facts, even although we may not yet be able to 

 apply rules for every case, — a subject which has been con- 

 sidered as highly important in its practical application to the 

 art of mining. 



The greatest controversy, however, relates to the mode in 

 which veins have been filled. Here, again, we must remark, 

 how the opinions of observers have been influenced by the facts 

 coming under their immediate observation. 



Werner, and the mining authors on whom he relies, drew 

 their inferences from metalliferous veins. Hutton and his fol- 

 lowers regarded chiefly those of another class ; and this great 

 author and his commentator Professor Playfair were evidently 

 ill informed as to metalliferous veins. 



That certain veins have been filled by injection from below, 

 and with matter in igneous fusion, seems to be rendered certain 

 by evidence, which is clearer than most we possess on such sub- 

 jects, and must be admitted at once. Thus, when we see a 

 trap dyke traversing a bed of coal and charring the combusti- 

 ble matter, and affecting the rock itself with visible effects of 

 great heat, we must assent to the cause assigned ; and when we 

 see matter of igneous origin not only filling the veins, but over- 

 flowing on the surface, or insinuating itself between adjacent 

 beds, the case is plainer than most that occur in geological re- 

 search. 



But though one class of theorists have proposed this as the 

 universal cause of the filling up of veins, ought we to admit this 

 to be true, when we find so many in which no similar appear- 

 ances are to be traced? 



Why, for instance, if the ores were forced from below, did 

 the power which injected them just limit itself to raising them 

 within a short distance of the surface, — for where shall we find 

 an instance of their being protruded above it ? 



If the metallic contents of veins were injected from below, we 

 ought to be able to trace something like the direction of the 

 currents in which the matter flowed ; we ought to see some 

 continuity in the operation, and some connexion between the 

 masses of ore which occur in veins ; whereas the contrary of 

 each is notoriously evident to every observer. 



It would seem also to be very probable, if the enrichment was 

 from below, and the matter was forced in from those regions 

 whence their treasures are supposed to be derived, that by a 

 nearer approach to the depths of the earth we should find the 

 riches more abundant. 



Professor Playfair admits this inference, and disposes of the 

 difficulty by arguing that it is so ; and says, that though mines 



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