476 PROCEEDINGS OF THE GEOLOGICAL SOCIETI. 



and flagstones unquestionably of Silurian age, having, where not 

 much fractured, the usual strike of N.N.E. and S.S.W., and cut 

 through by masses of porphyry and greenstone. Near some 

 points of contact, these schists are highly indurated, becoming 

 almost a Lydian stone, with pyritous crystals ; and in other 

 larger masses, particularly those which form the north-western 

 rock on which the north-western and southern bastions stand, 

 the rock is a gneiss, which, folding round points of green- 

 stone, can scarcely, if possibly, be mineralogically distinguished 

 from the oldest gneiss in the country. In receding, on the con- 

 trary, a few paces only from the most metamorphosed parts, you 

 pass into masses in which the lines of bedding and concretions are 

 distinctly visible, though the whole are much broken up, dip- 

 ping away to the E. and W. in truncated fragments of the harder 

 flagstone, wedged unconformably into the surrounding matrix of 

 schist. Transverse quartz veins are here nearly as abundant as 

 in the example at Bugten near the Egeberg. 



In taking leave of the sedimentary and metamorphic territory 

 of Christiania, with its encircling mountains of older or azoic 

 gneiss, I may state that, according to the views of modern geo- 

 logy, all the extensive tracts within that boundary, not merely in 

 the Christiania fjord, but also in the fjords of Drammen, Steen, 

 and Rand, and extending southwards to Frederiksvarn, compose 

 parts of a great palaeozoic basin, the base of which is the lowest 

 Silurian fucoid band, and its summit the old red sandstone. 

 This idea would, indeed, hardly strike any observer who looked 

 at M. Keilhau's map ; for, faithful as it is in respect to general 

 boundaries, the varied colours with which he represents the dif- 

 ferent granites, porphyries, and greenstones within the basin, and 

 the vast spaces overspread by those colours, necessarily withdraw 

 the mind from true historical considerations to features purely 

 mineralogical. 



The truth then is, that in some parts of this palaeozoic basin, 

 the strata of Silurian and Devonian age are abundantly developed, 

 though almost every where traversed by innumerable eruptive 

 dykes, and thrown about in rapid undulations, whilst in other and 

 still larger tracts, the eruptive rocks have usurped nearly the 

 whole surface, leaving mere shreds and patches only of the ori- 

 ginal sedimentary masses which once occupied the basin. Thus, the 

 granite which I have spoken of as piercing and metamorphosing the 

 Silurian rocks of Drammen, rises into mountains, and extends over 

 nearly the whole large promontory between Launig and Frederiks- 

 varn, ranging down to the sea in low and gnarled headlands, 

 exactly resembling those of Cornwall. Now, indeed, that we know 

 these intrusive Norwegian rocks to be posterior to the old red 

 sandstone, the analogy between them and the rocks of Devonshire 

 and Cornwall is very nearly complete. In both countries eruptions 

 have predominated, which I would venture to call " palaeo-plutonic," 

 to distinguish them from these more ancient granitic eruptions 



