Aug. 10, 1888.I 



SCIENTIFIC NEWS. 



139 



crystalline rocks are fusible, and that they are trans- 

 formed by fusion into a glassy mass. Some years later, 

 Spallanzani worked out a series of experiments on the 

 fusion of lavas, in order to destroy the reigning prejudices 

 on the cause of the heat of the eruptive matter. But the 

 chief honour is due to Sir James Hall, for the in- 

 auguration of geological research by means of numerous 

 celebrated experiments, which he generalised and applied 

 in the most masterly way. We can only consider here 

 that portion of Hall's work which concerns the synthesis 

 of rocks. About the time when Spallanzani was study- 

 ing by laboratory processes the conditions of the forma- 

 tions of lavas, the illustrious Scotch geologist fused some 

 eruptive rocks in a graphite receptacle, and observed 

 that the products of this fusion, if abruptly cooled, gave 

 an amorphous glassy mass, while a more gradual cooling 

 induced the formation of crystals. James Hall had al- 

 ready learnt from experience the principal basis for 

 future syntheses, viz., the fact that to reform crystals in 

 a fused rock, the glass resulting from this fusion must be 

 kept at a high degree of temperature, inferior, however, 

 to that originally required for the fusion of the rock. 

 During this annealing, certain minerals are able to crys- 

 tallise. These facts can be compared with those furnished 

 by recently ejected lava at the moment when the tem- 

 perature begins to fall. 



Towards the commencement of this century Gregory 

 Watt directed his researches into the same path ; he 

 experimented on a mass of basalt 700 lbs. in weight. He 

 fused it and let it cool down for eight days in a furnace, 

 which was allowed to cool slowly. During this prolonged 

 annealing spha:rulithic concretions, composed of radiating 

 fibres, about 6 centimetres in diameter, became isolated 

 in the black opaque glass obtained by the fusion of the 

 basalt, and finally this glass passed into a stony stage, 

 becoming granulated and charged withvery finecrystalline 

 particles. At the same time its magnetism increased and 

 its density grew from 2743 to 2 '949. 



One conclusion arrived at by Watt's research, which 

 resembled in many points that of Hall's, which we re- 

 ferred to above, is that while the molten mass is solidify- 

 ing crystallisation can take place. 



At the time when the path of the synthesis of rocks 

 was thus being prepared, analysis and other means of 

 investigation had not attained to the perfection of the 

 present day ; on the other hand, the prejudices which 

 prevailed in the earlier days of geology had accumulated 

 obstacles which were only surmounted at least half a 

 century later. We cannot pause here to survey the 

 brilliant period of mineralogical syntheses which followed 

 closely on the impetus given by chemistry and minera- 

 logy. It suffices to simply quote the names of Ebelmen, 

 Rose, Mitscherlich, Senarmonf, to recall to the remem- 

 brance all the remarkable results of the artificial 

 productions of minerals. But the researches of these 

 scientists had reference chiefly to the synthesis of 

 isolated specimens, and not to that of . rocks them- 

 selves, which are the aggregate of mineral specimens. 

 Generally speaking, these experiments were chiefly of a 

 mineralogical order, and only secondarily lithological. 

 Nevertheless, the efforts of these clever experimentalists 

 solved many a geological problem, and they also proved the 

 steady maintenance and accentuation of the tendency 

 which leads the intelligent to seek, by experimental means, 

 a more complete knowledge of natural phenomena. At 

 last, in 1S66, Daubrce reproduced crystalline rocks by 

 simple fusion, and it was his method which was finally 



adopted and developed by MM. Fouque and Michel Levy. 

 The researches of Daubree to which we here allude, are 

 those which he undertook in order to reproduce by fusion 

 certain meteoric stones characterised by the absence of 

 the feldspathic element. He fused an earthy rock, 

 lherzolite, whose composition resembles that of corres- 

 ponding meteorites, and succeeded in obtaining results 

 which, in the details of structure and composition, 

 faithfully reproduced those of the cosmic type which he 

 wished to imitate. 



At the time when this eminent geologist was thus an- 

 ticipating the researches which some years after were to 

 throw so brilliant a light upon the geological laboratories 

 of the College of France, the progress of the synthetic 

 method was still much hampered by hypotheses. It 

 was no longer those relating to the influences of mys- 

 terious forces that had to be dealt with, but the sup- 

 position that the reproduction of geological phenomena 

 in the laboratory was only possible at the expense of an 

 indefinite amount of time, and of temperatures and 

 masses of which, in the present day, we can scarcely form 

 an idea. It was thought then that the mineral combina- 

 tions in Nature followed other laws than did those 

 produced by chemistry. These prejudices, however, 

 were powerless to arrest Daubrce's progress on the 

 road, on which by his synthesis of meteors he had so 

 valiantly taken the first steps — for he, let us hasten to 

 observe, is one of those whose labours have done most 

 towards the eradication of these hypotheses from the 

 domain of geology. But the methods of analysis in vogue 

 in those days did not render penetration into the depths 

 of the natural rocks and subsequent comparison of their 

 internal structures with those of synthetic products at all 

 possible. The laboratories did not possess the necessary 

 apparatus for obtaining a very high degree of tempera- 

 ture or for maintaining it during lengthy experiments. 



The great improvements in the construction of appar- 

 atus, and the application of the microscope to lithological 

 work, have however facilitated the reproduction of all 

 contemporary volcanic rocks. Two French scientists, 

 M.M. Fouque and Michel Levy, who introduced micro- 

 graphical lithology into their country, commenced in 

 1877 a series of synthetic experiments, thenceforth 

 memorable in the history of science. One of them had ac- 

 quired a well-earned reputation by his remarkable works 

 on volcanic phenomena, which he had studied on the spot 

 in several classic regions ; he was familiar with all the 

 secrets of the chemical analysis of minerals, which he 

 carried out in the most ingenious and practical way. The 

 other, well -prepared by his studies in the French 

 colleges, had conducted with striking success an examin- 

 ation of minerals by their optical properties ; he had 

 carried on the application of exact methods in micro- 

 graphy further than had ever been done before, and had 

 already made himself known in the scientific world by 

 his researches on eruptive rocks of the ancient series. 



In their conjoint labours, MM. Fouque and Levy to a 

 certain extent systematised and arranged the facts relating 

 to the chronological succession of crystals in eruptive 

 rocks, and revealed a large number of the details which 

 we have already mentioned among the results of lava 

 analysis. It is to this happy association of talent, this 

 fertile collaboration, that we owe the great discoveries 

 which have rendered the College of France so celebrated, 

 and to which I am proud to render homage here in pre- 

 sence of an audience ever ready to welcome all scientific 

 progress, and at whose tribunal — the first in the world 



