S98 M. Keilhau's Theory of Granite, and other Rocks. 



which is best to be observed at the locality we have just named, 

 and where it occurs in the primary mica-slate ; between the 

 mass of porphyry and the mica-slate, there runs on each side 

 of the vein a zone or separating layer (Besteg) of greenstone, 

 about a foot in thickness ; and, indeed, at many points of the 

 same vein lying far from the one specified, the greenstone 

 shews itself in the same way and having the same thickness. 

 This singular phenomenon, Avhich, however, is not peculiar to 

 the iTiass of rhombic porphyry here mentioned, but occurs in 

 the case of several other abnormal formations of the territory, 

 must, according to the eruption theory, be explained in the 

 following manner: Either the greenstone must be considered 

 as belonging to a later intrusion, during which it found its way 

 up through clefts, which were formed by the separation of the 

 porphyry from the adjoining rock on both sides, or it must be 

 regarded as the effect of an earlier eruption, and was subse- 

 quently cleft through the middle, when the porphyry pressed 

 upwards and filled the newly opened fissure. 



We have now given the promised description. Nothing, so 

 far as I am aware, which can be adduced in favour of the vol- 

 canic theory of the massive mountain- rocks, has been passed 

 over ;* nor is there, on the whole, any thing wanting which is 

 generally brought forward in statements of this kind ; unless 

 it be, that we have not spoken of slags or of alterations by glaz- 

 ing and vitrefication ; but phenomena which are no where to be 

 observed, could not of course be introduced among actual facts. 



It is to be further remarked as to the representation we have 

 given, that the view which it exhibits to our eye, although it 

 is undoubtedly incomplete, as we shall soon see, yet, neverthe- 

 less, is in no small degree of exactness, a resemblance of the 

 original. At least a statement framed under the influence of 

 the other principal theory, viz., Neptunism, which considers 

 granite as a crystallization formed in and by means of water, 

 would not, by any means, have come so near the truth, and 

 could scarcely have included so many actual facts in its favour, 

 as have been here brought together. As to what relates to the 

 incompleteness of our volcanic description, this is partly owing 



' Our author uses the term volcanic in preference to plutonic. 



