M. Keilhau's Tlieory of Granite and other Rocks. 269 



adhere to a theory which seems to be the only one applicable 

 to at least the largest number, and the most important of the 

 facts which I have now adduced. 



We have still to consider the alterations in the stratified 

 rocks where these come in contact with other rocks, — namely, 

 with the abnormal rocks ; and to direct our attention to the 

 peculiar minerals which present themselves either at or neal* 

 the contact of the various masses which touch one another. 

 This study of both kinds of phenomena is that which leads 

 most directly to a knowledge of the forming and transforming 

 processes going on in solid rocks, without the aid of an extra- 

 ordinary degree of heat. That such processes have been espe* 

 cially active where heterogeneous masses met together, is to be 

 observed at innumerable points in new and old formations ; 

 and among these, there are frequently places where it is im- 

 possible to maintain that volcanic heat could have operated in 

 producing the phenomena in question. The relations present- 

 ed by these phenomena in the Christiania district, are of ex- 

 treme interest and importance ; they point to a much more 

 complicated play of forces than the mere action of a melted 

 mass on the bounding rock could have effected or produced. 

 These phenomena sometimes present themselves, and are some- 

 times absent, near the massive mountain-rocks ; sometimes also 

 they present themselves at the points of contact of stratified 

 rocks alone. The examples of the last mentioned appearance 

 presented by our district ought not to be passed over, although 

 they only contribute indirectly to the explanation of the real 

 subject of our investigation. Where transition-strata cover 

 the primary surface, which, as already mentioned, consist of 

 -tratified rocks, there is constantly an extraordinary quantity of 

 silica present, and metallic developments are observed at many 

 points of contact. By this unusual quantity of silica, are pro- 

 duced the number of quartzose masses which lie at the boun- 

 dary of the primary class, and with which the eurite-porphyry 

 series begins ; and to the same cause is undoubtedly to be at- 

 tributed the frequent occurrence of certain quartz druses in the 

 upper crust of the primary rocks, where the latter have been 

 covered by transition-deposits. Of ores, we met with accumu- ' 

 lations of magnetic iron-ore and copper- pyrites, which lie espe* 



VOL. XXV. NO. L. OCTOBER 1838. T 



