REPORT ON MINERAL VEINS. 21 



—of having operated at different periods, and of one having 

 produced effects for which another was inadequate. 



As we cannot easily conceive how the metahic ores can have 

 been deposited from solution in water, and appearances are 

 much against their having been injected in a state of fusion, 

 there is another supposition which, though not free from diffi- 

 culties, has yet probability enough in its favour to have gained 

 it many supporters, — which is, that these and some other sub- 

 stances have been raised from below by sublimation. This is 

 not a new opinion, for though the older writers expressed it in 

 an indistinct manner, and spoke of metallic vapours and exha- 

 lations, — and thus we shall find it proposed by Becher, Stahl, 

 Henkel, and others, — yet their meaning evidently was, that sub- 

 stances had been volatilized by heat, and assumed their places 

 in veins by condensation, or by combining with other materials. 



We know for certain that some of the metallic sulphurets 

 may be so volatilized, and will reassume their form and be 

 produced in a crystallized state ; and so far nothing is assumed 

 beyond our knowledge : but as we find these sulphurets, which 

 compose by far the greater part of the metdllic contents of veins, 

 in insulated masses, surrounded on all sides by other substances, 

 which we can hardly conjecture to have been sublimed, we en- 

 counter much difficulty in explaining how the process can have 

 taken place ; and it becomes even more difficult when we see 

 how very much these different classes of substances are incor- 

 porated, and how they completely, in most instances, envelop 

 and inclose each other. 



The hypothesis of filling up by sublimation would also seem 

 to require that the deepest portions of veins should be richer, 

 especially considering the very small extent to which after all 

 they have been perforated ; but yet, shallow as our workings 

 into the earth really have been, there is much appearance of 

 their having in many instances gone below the richest deposits 

 of the metals. 



This seems to have been the case in some of the deepest 

 mines in Mexico, and in several in our own country. It is im- 

 possible, indeed, to say that greater deposits may not exist still 

 lower down ; and though veins have not been traced to their 

 termination, they have in many instances been pursued until 

 the indications of metallic produce have become faint and hope- 

 less. And these unfavourable appearances have increased very 

 commonly with increasing depth, which is as much, perhaps, as 

 we are likely to know about it, as the operations of the miner 

 are thus arrested, and the inducement to further experiment is 

 taken away. 



