ON THE FORMATION OF CRYSTALLINE ROCKS. 255 



products of nature with those of the laboratory;* but it was under the 

 inspiration of Hutton that tlie first important synthetical experiments 

 were undertaken, t 



§ 1. Fufiion and cooling of rocks. 



Buffon had rigorously established, by direct experiment, that 

 granite and the principal crystalline rocks can be vitrified. He 

 thought that these immense masses of '■^natural glass'' had acquired 

 their crystalline state after very long annealing.:]: At the end of 

 the last century Sir James Hall, at the same time that he was study- 

 ing, as we have before seen, the combined influence of heat and 

 pressure on limestone, undertook numerous experiments with the 

 view of testing whether, as the adversaries of Hutton pretended, the 

 rocks formed by fusion should have remained vitreous. § He discov- 

 ered, as Buffon had foreseen, that certain silicates, instead of becom- 

 ing vitreous, may, by slow cooling, become crystalline and assume 

 a stony appearance, similar to that of eruptive rocks. These exper- 

 iments, which were continued b}^ other savants, proved further, that 

 a vitreous mass can even crystallize w^ithout passing through a state 

 of fusion.[| 



•^ " It will be, in our opinion, an important work, to carefully compare the products 

 taken from the bowels of the earth with those of laboratories ; for then will the striking 

 relations which exist between the products of nature and those of art be made visible to us. 

 Although the inexhaustible Author of nature might employ different means for bringing- 

 about what He wills, He delights in consistency amid the variety of His works; and to have 

 found the means of rej^roducing them is really a great step towards the knowledge of things. 

 NcUxire is only art on an extended scale." — [FTotogmi, French translation cited above, § 9.) "Do 

 not these general laws of the physical world operate in our laboratories as well as in the 

 interior of mountains?" — {Saussure, Voyage dajis les Alpes, § 750.) 



f The experiment by which Lemery, in 1700, tried to imitate volcanic phenomena, by 

 heating a mixture of iron and sulphur in damp earth, was founded on a false resemblance, 

 and only led to an entirely erroneous conclusion ; it made, however, a sufficient sensation 

 to justify an allusion to it. — (Memoires de I' Academic des Sciences, 1700.) 



\ Histoirenaturelledesmineraux. ^' These xnireous substances," he says, " melt without addition 

 at the same degree of heat as our artificial glass." Buli'un had, besides, remarked that feld- 

 spar is much more fusible than the other elements of granite. 



Leibnitz had, it is true, previously said that the earth and the stones submitted to fire 

 yield glass ; that glass is but the base of the earth, {Protogcea, § 3 ;) but he here confounded 

 all rocks, including limestone, silex, and sand, and there is a wide interval between this 

 Tague conception and the first precise experiments made by Buffon. 



I have mentioned above (chnpter iv, § 1) the experiments of Spallanzani on this subject. 

 We must also cite the experiments made by Butibn on the cooling of spheres of diiferent 



dimensions — some of metal, some of sandstone or marble — in order to represent the condi- 

 tions of the cooling of the terrestrial globe. Newton had before announced his intention 

 to make experiments of this kind. 



G Bischof, with the same end in view, made a series of interesting observations of the 

 fusion and cooling of spheres of basalt. ^ — {Die Wdrmelehre des innern Erdkcerpers, 1837, p. 

 443 to 505.) 



§ The experiments of Sir James Hall on the consolidation of basalts and melted rocks, 

 date 1800. — [Edinburg Phil. Trans., vols, v and vi.) 



II The experiments of Hall were continue.l on a larger scale by Gregory Watt. — [London 

 Phil. Trans., 1804, and Bihliotheque Britannique, No. 256.) At the same time Dartigues 



■ published his experiments on the devitrification of glass. — {Journal de Pharmacie, lix ; Journal 

 de Pht/iiqiie, Jx ; Annates de Chimie, vol. 1.) Fleuriau de Bellevue, sur I'action de feu dans 

 les volcans, Ix, 1805. Dree. Nouveaugendre de liquefaction ignee. — {Journal des Mines, vol. 

 xxiv, 1805 ; Mtmoires del' Acmemie des Sciences, 1805 ; JUemoires de l' Acadimie, 1739 ; London Phi- 

 losophical Tranntclions, 1776 and 1782 ) 



Eecent observations on devitrifications ^y Dumas and Pelouze, (Comptes Rendus, 1845, 1855, 

 1856,) and by Messrs. Mitscherlich, Gustave Eose, Charles Deville, and Delesse on the 

 fusion of rocks. 



