M. Keilhau's Theory of Granite, and other Rocks. 83 



ed the conversion of clay-slate into siliceous slate. There are 

 also to be found in our territory places where, in fact, the stra- 

 tified rocks in contact with granite do not merely exhibit the 

 usual degrees of alteration as flinty slate, striped jasper, &c., 

 but at length at the very boundaries present imperfect mica 

 and hornblende-slates, or even a sort of gneiss. But in these 

 cases there is always present a marked line of demarcation be- 

 tween such slates and the massive mountain-rock. It must 

 thus be admitted, that if the crystalline slate, which is in con- 

 tact with granite, and presents a sharply defined boundary, is 

 to be regarded as formed in the manner described, such an ex- 

 planation c^n by no means apply to the case where a complete 

 transition takes place ; thus, for example, at Solvsberg, we could 

 not say that a part of the granite which there presents itself is 

 directly pyrogenetic, and that the remainder, which affords 

 transitions to the slate, is indirectly pyrogenetic, being pro- 

 duced by the action of the other on the slate ; and we have 

 here the peculiar circumstance, that where both crystalline 

 mountain-rocks border on one another, they have so great a 

 resemblance that the difference cannot be observed, and thus 

 the boundary might easily be overlooked, should it not have 

 been really obliterated by these having been melted toge- 

 ther. Should any one now, further to support a preconceiv- 

 ed opinion, come forward with such an interpretation of the 

 transitions we have been considering, we have still another 

 fact of an analogous kind to bring forward, which scarce- 

 ly leaves the supporters of the volcanic origin of the rocks 

 in question any other mode of escape than that of which we 

 had formerly an example, namely, to deny the accuracy of the 

 observations. The phenomenon of which I speak is the fol- 

 lowing : there are places (for example on the Langesund-fiord*), 

 where the slate shining with microscopic crystalline particles, 

 lies as a bed of only one inch in thickness, between other sili- 

 ceous beds in which no crystalline structure has been develop- 

 ed, or between strata of limestone ; in other beds of the same 

 range of strata, and as little as the previous one in contact with 



• The Langesund-fiord is the next arm of the sea to the west from Fre- 

 deriksvaern, and has on its shores the towns of Laugesund, Brevig, and Pors- 

 grund — Edit. 



f2 



