48 (icology, as illustrated by Chemistry and Physics. 



these were lightly passed over. An unrestrained speculation, 

 wandering far beyond the limits of strict scientific investiga- 

 tion, went still further. What was supposed to have been 

 proved basalt of one species of a large class of crystalline 

 rocks was extended to all crystalline rocks. 



In the case of basalt, the analogy which it has with lava, 

 and the transition of the oue into the other, still remains a 

 leading fact. But this analogy is wanting in other crystalline 

 rocks ; for nowhere has a transition of lava, whether it comes 

 from extinct or still active volcanoes, into granite been met 

 with. 



Before taking such a bold venture as to declare granite, 

 syenite, and similar crystalline rocks, to be products of a 

 very gradual solidification of melted masses, the question 

 should have been asked, whether the order of successive 

 formation of the several mineralo^ical members of these 

 rocks represents their solidification.* If crystals of different 

 kinds, and different fusibility, were formed from a melted 

 mass, it is evident that the least fusible would be formed 

 first, and the most fusible last. Therefore quartz, the least 

 fusible member of granite, would have crystallised first; 

 feldspar and mica, being more fusible, would have crystallised 

 last. The latter two would naturally have occupied the 

 space left by the quartz. But, with the exception of the 

 graphic granite, in which quartz and feldspar appear as 

 simultaneous formations, precisely the contrary is found to 

 be the case ; the quartz occupies the space left by the crystals 

 of feldspar. Consequently the more fusible feldspar solidified 

 before the less fusible quartz. Fournet endeavours to re- 

 move this contradiction, by the assumption of a so-called 

 condition of supervision, according to which the less fusible 

 quartz is supposed to remain soft at temperatures far below 

 its melting point. But nothing is gained by this, more than 

 the support of one hypothesis by another. The one falls 

 with the other. 



But it is not for this reason alone that the hypothesis of 

 the igneous origin of granite falls to the ground. Other and 

 no less important evidence is opposed to it. 



* Lehrb. der Chemisohon u. Physik. Geologic, Bd. II., p. 923. 



