32-t THEORIES OF ORE DISPOSITION HISTORICALLY CONSIDERED, 



Unity less to the fact of having crystallized at great depths than to 

 its content of water (2 to 3 per cent), which enabled it to remain in a 

 pasty condition nuich below its fusion point, and thus alloAved quartz 

 to take the impress of other minerals. The minerals of the first 

 group of veins form part of the outer crust (j^enumbra) of granite 

 bodies, as granite once formed the outer crust of the earth. 



The products of volcanic eruptions he divides into two classes: 



(1) the lava-like, which consist of silicates in a molten condition; 



(2) the sulphur-like, which emanate in a molecular condition. To 

 the latter alone can the formation of vein minerals be attributed. 

 The term " solfataric,"' which was employed by subsequent writers 

 to describe the action of the sulphur-like emanations, has since been 

 very generally used by writers on ore deposits in a sense which is not 

 always strictly accurate. 



Although de Beaumont''s views are based on some premises no 

 longer considered tenable, they mark an important advance in this 

 line of research, in that they may be said to be the first fruits of 

 organized field investigation, for the first geological surveys, those 

 of Great Britain and of France, had been founded about ten years 

 before, and the first geological map of France had recently (1841) 

 l)een completed by the latter survey, of which he was the founder and 

 director. 



This was also an era of experimental investigation, as Avell as of 

 observation in the field. Following the example of Sir James Hall, 

 who had, as early as 1805, spent some years in experimenting on 

 the transformation of rocks under the combined influence of heat 

 and pressure, PVench geologists were actively employed in attempt- 

 ing, by synthetical expei-iment in the laboratory, to imitate the proc- 

 esses of nature in the formation of rocks and minerals, especially 

 of vein minerals. Prominent among those engaged in this work 

 were Berthier, Becquerel, Ebelmen, Durocher, Senarmont. and 

 Daubree. At first with heat alone and later employing heat and 

 water combined, ahvays under pressure, they succeeded in repro- 

 ducing artificially a great number of the minerals of rocks and veins. 

 Senarmont (1849-1851), by the aid of water at temperatures of 130° 

 to 300^ C, formed artificially 30 of the principal minerals found in 

 ore deposits, including quartz. The results of these experiments 

 did not, however, prove decisively the agents which nature has em- 

 ploj'^ed, since the}^ demonstrated that the same mineral may be formed 

 by several different methods. This was appreciated by Daubree, 

 Avho, connnencing his synthetical experiments with the artificial 

 production of cassiterite in 1844, carried on experimental investi- 

 gations into the mechanics of rock fracturing, the flow of subter- 

 ranean waters, and rock metauiorj)hisni in general to near the close 

 of the century. He was particularly impressed by his studies of 



