498 



volume of M. Burat's continuation of D'Aubuisson's Treatise on 

 Geology (1835), but it is now published separately, and gives the 

 clearest general view which I have seen of the application of geo- 

 logical theories to phaenomena observed in mining. It is written 

 by one who has acquired much practical knowledge as a miner, and 

 who is well versed in chemistry and mineralogy*. 



Werner, when he published his justly celebrated Essay on Mine- 

 ral Veins, had come to the conclusion that the same rent, after being 

 wholly or partially filled, has sometimes been reopened ; and M. 

 Fournet has endeavoured more fully to explain the successive dila- 

 tation of the same veins at distinct periods. He has given examples 

 in mines worked under his direction in Auvergne, in which the sul- 

 phurets of iron, copper, lead, and zinc, besides quartz, barytes, and 

 other minerals, seem evidently to have been introduced at different 

 periods by chemical action accompanied by new fractures and dis- 

 locations of the rocks, and the widening of preexisting fissuresf . 



You will find in M. Fournet's treatise a copious analysis of a great 

 variety of books on mining, besides a detail of facts which have 

 fallen under his own observation. He has described first those 

 veins which are decidedly connected with rents produced in rocks 

 by mechanical movements, and which are supposed to have been 

 chiefly filled from below by sublimation, more or less obviously con- 

 nected with volcanic action. He afterwards passes on to the con- 

 sideration of those masses which have been called stockwerks by 

 the Germans, which are imagined by some to have their origin in 

 the contraction of granite, porphyry, and other rocks as they cooled, 

 numerous rents being then formed, in which metallic particles were 

 concentrated. In treating the subject in this order the author ap- 

 pears to me to have followed the most philosophical course, begin- 

 ning with cases of undoubted rents of mechanical origin filled with 

 minerals and metals introduced by sublimation, and then carry- 

 ing with him as far as possible the light derived from these 

 sources to dissipate a part of the obscurity in which all theories re- 

 specting the nature of Plutonic rocks and their minerals must, I fear, 

 be for ever involved. Much will still remain unexplained; but 



* Etudes sur les Depots Metalliferes, par M. I. Fournet. 

 t See " Etudes," &r. Section 3. 



