M. C. Deville on the origin of Granite. 185 



original bath, have deposited these oxides of iron, of tin, of 

 titanium, these sulphides of molybdenum, topazes, tourmalines, 

 even phosphate of lime — in a word, this pleiad of bodies which 

 Humboldt has called the penumbra of granite, and on the forma- 

 tion of which DaubreVs experiments have thrown so much light ? 



Here, in fact, we meet with quartz. It is the most usual and 

 most abundant element of these deposits. It constitutes, so to 

 speak, the substance on which these varied minerals form a sort 

 of embroidery. But there can then be no doubt as to its origin. 

 It is a result of secretion. It is the product of molecular actions ; 

 and if, as everything tends to show, water has played a part in 

 these actions, this water must have formed an integral part of 

 the granitic magma, and separated in the state of fumarole, 

 carrying with it the other volatile elements of these reactions. 

 Here we have physical and chemical circumstances altogether 

 peculiar; we have a key to the explanation, furnished both by 

 observation and analogy, and which it is impossible not to take 

 into account. 



If to the physical properties of superfusible bodies, on which I 

 have dwelt at the commencement of this article, we add this 

 intimate association, this kind of combination, which it is im- 

 possible to deny, and which takes place under the influence of 

 particular and unstable causes between the mineral substance 

 and water or other volatile substances, why give up the expla- 

 nation of the formation of quartz and felspar by purely eruptive 

 phenomena ? Is there not an intimate association between the 

 two classes of facts ? Is not the faculty which a viscous body 

 possesses of assimilating liquids or gases, related to the abnormal 

 assimilation of heat which constitutes superfusion in viscous 

 bodies ? If I am not deceived, so long as these delicate points 

 of molecular statics are unexplained, it will be impossible to 

 affirm anything as to the present question. 



Before seeking to explain the formation of granite, let us try 

 to account for what takes place before our own eyes in a solidi- 

 fying lava. When we know something as to what influences the 

 division of the elements between the small number of minerals 

 formed, when we have some idea of the part played in these 

 curious phsenomena by the substances which gradually escape 

 in the gaseous form, it will be time to attempt the question on 

 its more complicated and difficult side. Only then shall we be 

 able to reason, without too great chances of error, on the cause 

 which, at the most ancient epochs of the globe, and under 

 physical conditions different perhaps from those of the present, 

 has produced, from the innumerable solid, liquid, and gaseous 

 elements of which we find the trace, the definite and stable 

 equilibrium from which granite has resulted. 



Phil Mag, S. 4. Vol. 20. No. 132. Sept. 1860. 



