528 Geology and Magnetism, 



New Grenada, Peru, Chili and the Brazils, similar channels of rocks 

 are equally productive. In a word, every mining district has its 

 conducting metalliferous channels, and the whole accumulated evi- 

 dence obtained in all parts of the world clearly proves the fact, that 

 the contents of the veins of fractures depend on the character of the 

 rocks they traverse, as represented in the sketches. 



It is of great importance to bear this fact in mind, because veins 

 which have been particularly rich at one place have led persons to 

 suppose that the continuation of the same fracture must lead to 

 more riches, although such a fracture may intersect barren rocks. 

 Every mining establishment ought to be in possession of the general 

 bearing and undulations of their respective metalliferous channels, 

 without which the work must be attended with great risks : guess 

 work, " where it is there it is" is an extremely bad principle to go 

 by, even with a good practical miner ; but when exposed to the 

 changes of agents, inexperience, &c, the consequence may be easily 

 conceived. After great expense has been incurred in carrying on 

 works through unproductive rocks, mines have frequently been 

 abandoned, when within a few feet of rewarding our search, for the 

 want of knowing the width and positions of the barren and rich 

 channels of ground. On the other hand, in prosecuting works of 

 discovery in a direction where no metalliferous channels exist, mines 

 have been carried on at a considerable loss, simply because the vein 

 happens to be in the same direction as another more productive. 

 Of all speculative employments, mining has been, and continues to 

 be, for the want of a well-founded principle, the most uncertain ; 

 experience and ingenuity being frequently and completely defeated, 

 although the miner has been continually led to suppose himself 

 on the point of meeting a good course of ore ; while from veins, 

 which men of equal ability have abandoned, large profits have after- 

 wards been realized. Therefore the theory of the formation of 

 mineral veins, and the rules which lead to the discovery of the 

 richer deposits, are objects of much greater national importance than 

 is generally supposed. It is essential to the interest of every 

 mining proprietor to know the general character of the local dis- 

 semination of the minerals in the district, and indispensable to his 

 forming a correct judgment on the mode of working adopted by 

 the practical miner. 



