1845.] ^07 



been formerly much laid open by quarries, has led to a thorough 

 acquaintance with the nature of its junction with the granite. 



Unaltered strata. Red Granite. 



Among other geologists, Professor Naumann of Saxony observed 

 this junction some years ago, and showed that just in proportion 

 to its contiguity to the granite, has the limestone been altered ; 

 veins of granite having actually been found by him intruded into 

 the calcareous mass. Though such a junction was no longer 

 visible, we had great satisfaction in observing the extent to which 

 so large a mass of limestone (laid open in extensive quarries 40 

 to 50 feet deep) had passed into a state of marble, particularly in 

 its lower parts, and still more in detecting in one of the depressions 

 adjacent to the quarries, and not far from the intrusive rocks, 

 portions of the limestone which were thickly impregnated with 

 crystals of garnet, and other parts where the sandy shales and 

 calcareous courses are welded as it were together, with few or no 

 traces of bedding ; the mass having assumed the aspect of a com- 

 pact garnet rock similar to a variety with which I am acquainted 

 in the Ural Mountains.* 



On receding from these promontories of granite, the strata resume 

 their natural characters : the beds of limestone are clearly divided, 

 other included Pentameri appear, the flinty slates become ordinary 

 black schists, and the whole group, though never free from great 

 undulations, resembling in this all the Silurian islands of the bay, 

 puts on all the characters which are peculiar to it in Christiania 

 fjord, to which I have now reconducted my readers, after a rapid 

 traverse across the high plateau of Ringerigge, and a survey of the 

 eruptive rocks as seen around its external edges. 



Conversion of Lower Silurian Schist into mock Gneiss. — If the 

 granite of Drammen has altered sandstone into quartz rock, and 

 Pentamerus limestone into marble with garnets, the greenstones 

 and poi-phyries of Christiania, particularly on the eastern side of 

 the bay, have produced a still more remarkable change on fucoid 

 shale, transforming it into a rock which might very well be mis- 

 taken for old Azoic gneiss. 



The spot where I first observed this phenomenon in company with 

 Professor Forchhammer, is on the sea-shore at the southern foot 

 of the Egeberg, where a little promontory stands out in advance of 

 the mountain of ancient gneiss, and juts out into the bay, in 

 which there are several little islands as well as a low tongue 

 of Silurian schists and flagstones. 



* Some of this rock was in the mineral condition of " Allochroite," according to 

 Professor Forchhammer. 



