ON THE FORMATION OF CRYSTALLINE ROCKS. 245 



giving it precision and at the same time supporting and developing 

 it by numerous and exact observations.* 



It was discovered, besides, that the formation of thermal and gaseous 

 springs, as well as of metalliferous veins, had some connexion with this 

 system of fracture, even in regions which are not traversed by erup- 

 tive rocks, t 



§ 5. Internal heat of the earth proved by direct measurement. 



Although the internal heat of the earth forms the foundation of the 

 entire system of Hutton, it was not until later that this capital fact 

 was verified in a positive manner, that is, by measurements suffi- 

 ciently exact and numerous enough to establish the truth of it beyond 

 a doubt. By an exception which is rare in the sciences of observa- 

 tion, speculative ideas, had, in this particular case, anticipated the dis- 

 covery of the reality. Before the first memoir of Hutton there ex- 

 isted scarely anything relative to the increase of temperature below 

 the earth's surface, but the observations cited by Kircher in 1644, :[: 

 and those made by Gensanne in 1749, in the mines of Giromagny. 

 The measurements made in Saxony by Freiesleben and Humboldt 

 date from 1791; they were, therefore, only anterior to the second 

 edition of the work of the chief of the Scotch school. From this time 

 observations have succeeded one another in great number up to the 

 present day; the principal of which are due to Aubuisson, de Trebra, 

 Arago, Duiong, R. Fox, Boussingault, Reich, Delarive, Ermann, Wal- 

 ferdin, and some others. There were still, however, causes of error 

 which raised objections to the main fact, when Cordier, in his 

 essay on the temperature of the earth, (read in 1823 before the Academy 

 of Sciences, and published in 1827,) overcame the last doubts. Be- 

 fore this publication, this savant, whom the aspect of Teneriflf had 

 long before confirmed in the ideas which he had imbibed from Dolo- 

 mieu, had rigorously determined by the aid of a new process of analy- 

 sis the mineralogical constitution of volcanic rocks, and the analogy 

 which unites them all, even when they are of a different composition.§ 



Finally, we know that several geometricians have sought to study by 

 calculation the condition of the interior of the globe at different epochs. 



* The superposition of granite and porphry in the formations of transition of the environs 

 of Christiania, which Haussmann. observed in 1805, and the slow and gradual risiug of the 

 soil of Sweden, were irresistible arguments to Leopold de Buch. 



Among the oldest observations of tlie same kind we must cite those of Count Marziiri 

 Pencati, who had accompanied Fonjas 8aint Fond to Italy, and who had given his atten- 

 tion to the superposition of the rocks reputed primitive and to stratified formations, par- 

 ticularly in Southern Tyrol, (1819.) 



t Hoffman was one of the first to clearly point out this relation for the gaseous springs 

 of the north of Gerniauy. — {Nordwesthches Deutschland, 1830 ) 



X The same year that Descartes published his ideas on internal heat. These first experi- 

 ments are due to Schapelmann, Bergrneister at Schemnitz, in Hungary. 



§ Recherches sur Ics diff^rents produits des volcans. — (Journal des Mmes, vol. xxi, j). 249, 

 1807 ; vol xxiii, p. 35, 1808.) Memoire sur les substances dites en masse qui entrent dans 

 la constitution des roches volcaniques de touts les ages. — (Journcd de Phybque, vol Ixxxiii, 

 1816.) 



