82 M. Keilhau^s Theory of Granite^ and other Rocks. 



tification is particularly well marked. In another portion we 

 still detect the parallel structure, but in the mass which in the 

 preceding specimen seemed homogeneous, there now glimmer 

 fine particles that in the following fragment are to be recog- 

 nised as plates of mica, and in the succeeding one there also 

 occur portions of felspar, and so forth ; — in short, there is to 

 be observed a gradually advancing development from compact 

 slate to a large-grained granular rock, which Von Buch has ex- 

 pressly termed granite. But, however convincing our suite of 

 specimens may be, it is so but in a small degree, compared 

 with the sight of these phenomena in nature itself; for on the 

 spot we can distinctly remark this circumstance, that the transi- 

 tion is by no means sudden, but extends over a long distance. 

 We can plainly see how gradually it lakes place, and that thus 

 the stratification and fossils disappear only by little and little, 

 and all in proportion as the compact structure is converted in- 

 to one which is more crystalline-granular ; and I have no doubt 

 that every one who will bestow sufficient time and attention on 

 the investigation, will not only be able to follow the parallel lines 

 of the undisturbed direction of the slate beds into that region 

 where granitification has already distinctly enough made its 

 appearance, but will detect traces of petrifactions where the 

 siliceous masses present shining microscopic crystalline grains ; 

 and the same is the case in specimens from another analogous 

 locality. 



The boundaries of the granite and slate are not everywhere 

 such as we have now described them. The occurrence of ra- 

 mifications at the boundary is certainly the most usual ; but 

 still it is not exclusively the appearance presented ; for at some 

 points at least, instead of such a phenomenon, we find perfect 

 transitions between the granitic formations on the one side, and 

 the siliceous slates on the other. 



Similar transitions can also be pointed out under entirely 

 different circumstances. These are of importance with respect 

 to an objection that might be made regarding the phenomena 

 just described. The opinion has been started, as we shall see 

 better afterwards, that felspar and the other component ingre- 

 dients of crystalline slates have been developed by the opera- 

 tion of the melted masses occurring in their vicinity, i. e. by 

 means of the same causes as have been supposed to have effcci 



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