S96 M. Keilhau's Theory of Granite and other Rocks. 



of ironstone (magnetic iron-ore) considerable enough to be re- 

 garded as an object for mining operations. The mine which 

 owes its existence to this remarkable appearance, and where one 

 can observe the phenomenon inaconvenient and convincing man- 

 ner, is that of Aaserud, below the Eidsfoss works. We have then 

 in tliese greenstone veins three of the appearances which are con- 

 sidered as proofs of their Plutonian origin ; the included frag- 

 ments, the alterations of the bounding strata, and the forma- 

 tion of particular substances at the line of contact. A fourth 

 phenomenon, which is regarded as the consequence of the sup- 

 posed eruptions, viz. disturbances in the position of the neigh- 

 bouring strata, has hithei'to not been any where observed. 



It has been stated that greenstone also assumes the form of 

 beds. This, it is true, cannot be denied ; but from some ex- 

 amples it would appear that, if we could trace such masses far 

 enough, we should probably in most cases find deviations, in 

 consequence of which they would be better described by the 

 term jfilons-couches, employed by some French geologists. 

 Thus, there is an example on Langoe, near Holmestrand, of a 

 mass of greenstone, which for a long distance lies quite parallel to 

 the slightly inclined strata of the hanging and lying sides ; but 

 afterwards it suddenly deviates downwards on the lying side, 

 and then this vein-like included mass is continued again as a 

 bed within the stratum which formerly belonged to the lying side. 

 There are cases, besides, where masses which for a long way have 

 continued as beds, at once forsake this form, and become forked, 

 which, however, often happens in such a manner that the por- 

 tions separated by the bifurcation again run on as thinner beds. 

 According to the eruption theory, these must be admitted to be 

 the results of pi'essings in from the side. It deserves here to 

 be remarked, that greenstone never exhibits those generally thin 

 ramifications penetrating the contiguous rocks in all directions, 

 which are so common with granite and syenite. The same is 

 the case also with the porphyries. As the cause of this, it 

 would be easy to assign a difference in the degree of fluidity 

 in the respective formations at the time of their appearance, 

 viz., that the greenstone and porphyry were more viscid, that 

 is, less fluid than the granite. 



Rhombic Porphyry. — We have still one species of abnormal 



