THE SCIENTIFIC PEKIOD 17 



This was also an era of experimental investigation, as well as of ob- 

 servation in the field. Following the example of Sir James Hall, who 

 had, as early as 1805, spent some years in experimenting on the trans- 

 formation of rocks under the combined influence of heat and pressure, 

 French geologists were actively employed in attempting, by synthetical 

 experiment in the laboratory, to imitate the processes of nature in the 

 formation of rocks and minerals, especially of vein minerals. Promi- 

 nent among those engaged in this work were Berthier, Becquerel, Ebel- 

 men, Durocher, Senarmont, and Daubree. At first with heat alone and 

 later employing heat and water combined, always under pressure, they 

 succeeded in reproducing artificially a great number of the minerals of 

 rocks and veins. Senarmont (1849-1851), by the aid of water at temper- 

 atures of 130° to 300° C, formed artificially thirty of the principal min- 

 erals found in ore deposits, including quartz. The results of these 

 experiments did not, however, prove decisively the agents which nature 

 has employed, since they demonstrated that the same mineral may be 

 formed by several different methods. This was appreciated by Dau- 

 bree, who, commencing his synthetical experiments with the artificial 

 production of cassiterite in 1844, carried on experimental investigations 

 into the mechanics of rock fracturing, the flow of subterranean waters, 

 and rock metamorphism in general to near the close of the century. 

 He was particularly impressed by his studies of the mineral processes 

 that have gone on since Roman times in the masonry of old thermal 

 establishments at Plombieres, Bourbonne-les-Bains, and elsewhere, in 

 which he thought to trace the actual processes of vein formation. His 

 works, " Experimental Geology " (1879) and " Subterranean Waters " 

 (1887), which contain the first philosophic discussion based on experi- 

 ment of the physics of the rock fractures that constitute canals for the 

 circulation of underground waters, are still classic works of reference for 

 the students of ore deposits. Daubree understood veins to be fractures 

 formed by dislocations of the earth's crust under pressure strains and 

 filled by deposits from aqueous solutions, generally heated by contact 

 with igneous rocks, from which in certain cases they may have directly 

 emanated. From his observations at Plombieres he inferred that most 

 minerals are soluble if given sufficient water and time, and that great 

 heat and pressure are not absolutely necessary prerequisites. Some of 

 the materials of veins, he admitted, may have been derived from the 

 surrounding rocks. 



The middle of the nineteenth century was characterized by the in- 

 creasing use of laboratory experiments [in chemistry and physics as 

 aids in testing the current theories of vein formation, as is shown in the 

 preceding sketch of progress of opinions among French geologists. 



Similar progress was going on in other countries, especially in Ger- 



III— Bull. Geol. S'oc. Am., Vol. 15, 1903 



