106 VEINS THEIR NATURE AND ORIGIN. 



"be the repositories of other kinds of ore. As the main 

 veins or "lodes" are thus intersected by others of more 

 recent date, they will also be more or less displaced, and 

 the ascertaining of these facts is ever of the highest 

 moment to the mining industry of a district, to say nothing 

 of its importance to correct geological deduction. The 

 mapping of these directions and the colouring of the 

 primary and secondary veins according to the kind of ores 

 they contain, is a work to be done by the mining-engineer 

 for each respective district ; though it is now well known, 

 that according to the rocks of a country and the age and 

 direction of its hills, so also are the general strikes of the 

 veins and the nature of their metalliferous contents. The 

 direction of veins and the nature of their contents reveal a 

 chronology and order within their respective areas as much 

 as the stratified systems do, and a knowledge of these rela- 

 tions is alike of scientific and economic importance. 



At the present time attention has been less directed to 

 the direction of veins and the corresponding nature of their 

 contents than to the modes of their formation and their 

 subsequent infiltrations. At one time igneous action was 

 called in by hypothesists, not only to produce the original 

 fissures, but to accomplish also the subsequent fillings-in ; 

 and, in fact, to perform the most opposite and contradictory 

 functions. Now, however, while it is agreed that the rents 

 and fissures were originally produced by, and owe their 

 linear directions to, vulcanic commotions, it is the general 

 and growing opinion that their subsequent fillings-in with 

 sparry and metallic matters are due to the infiltration and 

 deposition of chemical solutions. Heated waters and va- 

 pours, or hydro-thermal action, as it has been termed, has 

 been the main agent in dissolving, carrying upwards, and 

 re-depositing the mineral and metallic matters that is, the 

 sparry vein-stuffs as well as the crystallised ores. In fact, 



