Dr. Mac Culloch on Mineral Veins. 189 



remembered, that a vein must traverse every rock that was in 

 existence at the time of its formation. The vein that intersects 

 the granite, intersects the superincumbent strata also; and tin, 

 copper, or lead, as it may happen, v?ill occur in every part of it. 

 It may have required uncounted centuries to form all the strata, 

 but the vein is, comparatively, the work of a moment. It is a 

 separate question, to what extent the adjacent including strata 

 modify the contents of their veins ; and it is one that will be 

 examined hereafter. 



Lastly, to attempt to classify metallic veins according to the 

 nature of their contents, is to make arrangements worthy only 

 of the cabinet mineralogist ; systems which philosophy dis- 

 claims. If there were an hundred, for example, instead of ten 

 or sixteen lead-glance formations, we must be content to re- 

 main ignorant of the ages of all that we cannot prove by the 

 incontrovertible marks already indicated. 



There is not one circumstance, in the history of veins, whether 

 we regard their forms, positions, seats, origins, or the nature 

 and disposition of the minerals which they contain, which can 

 entitle us to conclude that they possess a resemblance or ana- 

 logy throughout the world ; that they are of definite and de- 

 finable ages ; or that they are, in any sense of the word, gene- 

 ral or universal. Yet this doctrine is supported by geologists, 

 who imagine that the mines of New Spain are similar to those 

 of Hungary and Saxony. That Patrin, who had imagined the 

 earth organized and endowed with a vital principle, should pro- 

 tract a zone of copper, silver, and lead, from England through 

 Europe, Asia, and America, may be excused. But it is an 

 abuse of the term generalization, to extend it alike to the 

 visions of theorists and the inductions of philosophers. 



Of the Seats and of the Contents of Mineral Veins. 



The nature of the rocks in which mineral veins are found, is 

 in every respect an interesting object of inquiry ; but it is neces- 

 sarily very limited, and, what is worse, cannot be converted to 

 any useful purposes. They may be said rather to belong to 

 countries than to rocks ; since, in one, that substance may be 



