M. Keilhau's Theory of Granite, and other Rocks. 395 



of these bed-like masses of porphyry, with regard to their 

 boundary relations and their position, answer in the most com- 

 plete manner to the conditions which are so far required for 

 true beds ; yet, there are not wanting deviations in this respect. 

 On the western boundary of our geological territory, there is a 

 bed of porphyry seven English miles wide, at whose regular in- 

 tercalation in the alum-slate for great distances we cannot but 

 be surprised ; but at one place there is distinctly to be observed, 

 a short and thick outrunner, by which the mass descends intO' 

 the subjacent bounding rock ; irregularities of other kinds are 

 to be found in others of these porphyry masses. 



While eurite-porphyry most commonly occurs in the form 

 of more or less perfect beds, and is found only as an exception 

 in the foriu of veins, the reverse is exactly the case with re- 

 gard to the greenstones, viz. Diorites and Aphanites. These 

 rocks, which in some places represent basaltic masses, are to 

 be seen at many points near Christiania, forming nearly verti- 

 cal veins, which pass almost at right angles through beds of 

 limestone or clayslate. These continue likewise beyond the' 

 boundaries of the transition series, and a few of them can ac- 

 tually be traced into the primary formations. It must be with 

 the greatest possible satisfaction that the supporters of the py- 

 rogenetic theory of the massive mountain-rocks survey these 

 veins, for not only does the last-mentioned fact support their 

 opinion, that the greenstones have been pressed up through 

 clefts in the primary ibrmations to and through the transition 

 strata ; but, further, portions of gneiss and other fragments 

 torn from the primary rocks, ai'e found in the greenstone veins,. 

 and that too even within the limits of the transition territory. 

 In some places, also, we find that the slate is indurated, and 

 the limestone impregnated with silica, at the junction with: 

 these masses of greenstone ; and we are acquainted with one 

 vein of this sort which is perfectly analogous to that neai* As- 

 chafFenburg in Germany, which we cited when treating of the 

 variegated sandstone formation, and which is accompanied bjs 

 a separating mass (bestegjbrviig Masse*) of brown ironstone. 

 Like it, our vein has immediately at its side a continuous mass 



" Besteg in German and Danish, and corresponding to lisiere in P'rench, is 

 the term e II plovel to denominate the ted or layer which sometimes sepa- 

 rates a vein from the rock in which it is containe.l.'— Edit. 



