certain Metalliferous liepoaitoriea in Depth, 235 



the vein. In some mines the substitution is complete. It 

 is now no longer doubted that all the repositories oxidated 

 and carbonated at the surface are transformed in the deeper 

 parts into sulphuretted minerals. Now, if the sulphurets must 

 be ascribed to phenomena acting from below upwards, it is 

 difficult not to suppose the same origin for the carbonates, 

 oxides, and silicates. 



This theory being once admitted, it only remains to com- 

 plete it by explaining the differences pointed out in the com- 

 position. In the calamine repositories the explanation is 

 afforded by the very nature of the filling up ; all the upper 

 part has been filled under the mingled influences of subter- 

 ranean and sedimentary actions, while below the inferior 

 emanations have acted exclusively. 



The calamine repositories of Silesia, studied by M. Delesse, 

 have suggested analogous ideas to him. 



In the Sierra-Morena the repositories of Los-Santos pre- 

 sent us with an analogous example. A vein of large di- 

 mensions, at least in the upper parts, consists of a mixed 

 composition, in which the phenomena, not of an arenaceous 

 sediment, but of chemical precipitation from a calcareous 

 travertin, has taken as great a part in the filling up as the 

 subterranean emanations which produced spathic iron and 

 copper minerals. (See the Supplement to the Etudes sur les 

 Mines.) 



From examination of the mines of Chili, M. Domeyko has 

 come to the conclusion that the chlorides of silver, which are 

 abundant at the surface, were replaced below by sulphuretted 

 minerals ; and that this modification resulted, not from pos- 

 terior actions, but from actions coeval with the formation of 

 the repository. The same explanation has been applied to 

 the repositories of argentiferous paces and colorados of 

 Mexico and Peru, which, in the deeper parts, are transformed 

 into tiegros, that is to say, into sulphuretted minerals. 



We conclude, then, that the differences of composition ob- 

 served in many repositories, when we compare the levels, 

 result from this, that the metalliferous emanations are modi- 

 fied on approaching the surface, under the influence of waters 



