300 M. B. Studer on the Origin of Granite. 



on the walls of furnaces ; and hence it has been supposed that 

 every transformed mountain-mass must have been in contact 

 either with apparent or concealed plutonic rocks. It is quite 

 possible that high temperatures may have essentially contri- 

 buted to the process under review ; but, in otlier respects, the 

 adduced comparison appears exceedingly defective ; and chief- 

 ly, as it has often enough been stated, because the influence 

 of the dykes, extending at most but a few feet, bears no pro- 

 portion to the metamorphosis of a whole mountain. Besides, 

 our physical and chemical theories are in most cases satisfac- 

 tory in the explanation of the observed influence, whilst the 

 metamorphosis of the Fli/sch-rock into gneiss or serpentine is 

 based merely upon hypothesis alone. But the complete dif- 

 ference of the two processes is made evident by the simple ob- 

 servation, that ivt so far as the crystalline silicates have been 

 produced from sedimentary deposits, we cannot ascribe the me- 

 tamorphosis to their influence, that is to say, to their own pro- 

 duction. There is still another fact, hitherto little insisted on, 

 which appears to denote a very striking difference between 

 the two appearances ; for it seems quite incompatible with this 

 theory of contact, that in the Alps, at all events, the change has 

 peculiarly manifested itself in the external and higher masses, 

 whilst the inner and deeper strata are nearly unchanged, — 

 the rocks in which the metamorphosis is most conspicuous, 

 are entirely separated from the alleged sources of the change 

 by great masses more than 1000 feet thick, and without our 

 being able to perceive any internal or concealed uprising of 

 massive rocks in the form of veins. Thus, in the Southern 

 Alps, dolomite forms the highest rocky precipices ; and it is 

 only after passing over a long range of stratified deposits 

 which contain fossils, that we descend to the red or black por- 

 phyries. And how striking is it that in those places where 

 the different kinds of rocks are in juxtaposition, as at Pre- 

 dazzo, the limestone passes not into dolomite, but into granu- 

 lar marble ; exactly as in the Grisons, where the limestone 

 lying close upon serpentine, or surrounded by it, is always free 

 from magnesia, though often white and transparent, like a pro- 

 duct of contiguity : at a somewhat greater distance, the same 



