360 M. Amedee Burat on the 



Stolberg, &c., ascribe this want of success only to the insuf- 

 ficiency of the works, and not to any defect in the principle. 



Besides all this, subterranean investigations are now suf- 

 ficiently advanced to authorise us to suppose that, at consi- 

 derable depths, the oxides and metalliferous carbonates which 

 constitute these repositories, must be transformed into sul- 

 phurets. These superficial masses, consequently, could only 

 be the highly-developed yossaw of subterranean repositories, 

 composed of pyrites, blende, and galena. Modern metallurgy 

 can treat blende as well as calamine, insomuch that we may 

 consider the continuation of the mineral as certain ; but, ten 

 years ago, this change of nature would alone have been 

 sufficient to make us declare the mineral limited in depth. 



Such, in fact, is the history of the pacos and colorados of 

 the New World. Many of these repositories have been con- 

 sidered exhausted, solely because the metallurgic resources 

 of these countries could not derive, from the sulphurets found 

 at great depths, the same portion as from the oxides of the 

 surface. 



Irregular repositories, which have performed so important 

 a part in tiie production of metals, long remained in an aban- 

 doned state, for this reason, that they were the first that 

 were mined. The ancients had removed the upper parts, 

 and were arrested by the difficulties of deepening ; for, in 

 these repositories, sterility often succeeds the utmost pro- 

 ductiveness. These ancient mining woi^ks now only appear 

 as superficial depressions caused by the falling in of the 

 subterranean works, or irregular empty spaces, partly rem- 

 hlayes, communicating with each other by narrow and sinu- 

 ous conduits, the walls of which were completely stripped of 

 minerals. The re-opening of these mines is often very hazard- 

 ous, for the rules that regulate veins cannot be applied ; and it 

 is often very difficult to explain the law according to which the 

 minerals are distributed. Many attempts, however, have 

 proved fortunate ; and the mines of Santiago de Cuba, accord- 

 ing to documents which have been communicated to me by M. 

 Arrieta, appear to furnish one of the most interesting argu- 

 ments for the principle of continuity in deptli, applied to ir- 

 regular repositories. 



