242 EXPERIMENTS ON METAMORPHISM AND 



nomena have their origin under granite and the other primitive forma- 

 tions; that is to say, below the solid crust of the globe.* This idea, 

 with which we are now so familiar, appeared new at an epoch when 

 volcanic eruptions were generally considered as isolated, superficial, 

 and insignificant accidents. In fact, the experiment of Lemery on 

 the spontaneous combustion of a heated mixture of sulphur and 

 iron,t or the supposition of the subterraneous conflagration of car- 

 bonaceous combustibles sanctioned by the almost sovereign authority 

 of Werner, had led everywhere to the assignment of some local focus 

 as the cause of these phenomena. Buflbn himself, the most ardent 

 promulgator of the primitive heat of the globe, took no other view 

 of them. Thus the grand idea of Descartes, which had thus early 

 connected these phenomena with the formation of hot springs and 

 metallic veins, and even with ancient fractures of the earth's crust, 

 had passed into an oblivion scarcely conceivable. And it was by 

 being brought back to this idea through the force of facts that Dole- 

 mieu contributed so much to the rapid advance which geology then 

 made in France. 



But the human mind is in general not freed from erroneous ideas 

 except by long and successive efforts. It Avas then believed, and 

 Dolemieu sought to explain it by unfounded hypotheses, that lavas, 

 instead of deriving their heat from internal fires, acquire it by a sort 

 of interior combustion which they undergo on arriving in the atmos- 

 phere; that, moreover, they are kept liquid by some kind of flux, 

 such as sulphur. It was necessary that Spallanzani should perform a 

 long series of experiments on the fusion of lavas in crucibles and 

 glass furnaces to overthrow these prejudices. | The exactitude and 

 the genius for observation of the illustrious professor of Pavia showed 

 itself in his studies on the nature and origin of volcanic rocks, as well 

 as in his brilliant discoveries in animal economy; and he is one of 

 those who had the merit of introducing the experimental method in 

 geology. § Since then Alexander Von Humboldt, after having ex- 



* 1st. The products of volcanic action belong here (in Auvergne) to a mass of matter 

 which differs from the granites and lies below them. 2d. Volcanic action has exerted itself 

 here under the granite, and has been at work in the depths much inferior to it. 3d. 

 Granite is not the most ancient rock, since it is of necessity posterior to that which sup- 

 ports this mass. — (Report made to the Institute on the travels of the years 5 and G, Jour- 

 nal d.es Mines, vol. 7, p. 397, 1798.) 



A few lines further on (p 39S) Dolomieu adds, " that there are reasons for extending these 

 conclusions to all other volcanoes, without regard to the nature of the soil that sur- 

 rounds them. Volcanic agents everywhere have their seat at great depths below the con- 

 solidated crust of the earth. 



fMemoires de I'Academie des Sciences, 1700. 



Afterwards Pallas was led to refer the cause of volcanoes to the crystalline schists con- 

 taining pyrites, like those he had had an opportunity of seeing in the Ural. 



:j: Voyage dans les Deux Siciles, 1792, introduction and fourth volume. 



§ Spallanzani further discovered the marine acid (chlorhydric acid) among the gases 

 which puff up the lavas, and hydrogen in the natural fires of Barigazzo. 



In closing his observations on lavas, Spallanzini reproduces this remarkable opinion of 

 Faujas-Saint-Fond. "It is not impossible that water united with fire njay bring about 

 combinations unknown to, and unattainable by art." — (Vol. iv, p. 75.) 



