1855.] MURCHISON — CHRISTIANIA. 165 



he says, everywhere overlies the Upper Silurian, and to which he 

 assigns a thickness of 900 feet, M. Kjerulf attributes the absence of 

 fossils (none having been found in it) to a contemporaneous volcanic 

 or igneous action, which caused a deposit of the tufaceous matter 

 whereof the Lower Devonian is composed. The higher parts become 

 more sandy ; grains of quartz appearing, and finally a coarse red 

 conglomerate. 



Some peculiarities of the trap and porphyry districts are mentioned, 

 and the cavities of the amygdaloid (mandelstein) are said to be often 

 occupied with natrolite, green-earth, calc-spar, fluor-spar, striped 

 chalcedony, quartz, prehnite, apophyllite, and sometimes with curious 

 nodules of anthracite in calc-spar. Breccias appear in great force ; 

 one of these occurring between the Old Red Sandstone and the 

 augite-porphyry, and another between the augitic and the felspathic 

 porphyry. It is further stated, that there is no silicification of the 

 slates or limestone in contact with granite or porphyry ; the first 

 being simply indurated, and the second converted into marble. 



Some other structural phsenomena are briefly touched upon, 

 among which it is said that the veins proceeding from granite appear 

 to be of augite-porphyry, and that the veins emitted from the syenite 

 are of felspar-porphyry. 



For my own part I have merely to state that, as far as I am 

 acquainted with them, the observations of Mr. D. Forbes and 

 M. Kjerulf are in unison with the opinions expressed by M. Forch- 

 hammer and myself, particularly in respect to the metamorphosed 

 schists, sandstones, and limestones of Silurian age, and also in demon- 

 strating that the chief outbursts of the igneous rocks of this region, 

 and specially of the porphyries, were posterior to the deposit of tlie 

 Old Red Sandstone. 



In conclusion, let me say that, although I failed in leading Prof. 

 Keilhau to agree with me respecting the order of succession from 

 flanks to centre, or in the identity in age of his " harte schiefer " 

 and my Lower Silurian, it was the simple inspection of his own geo- 

 logical map of the Christiania Territory which first led me to entertain 

 views which I realized by personal surveys. By inspecting the map of 

 Keilhau, the geologist will see, that the whole of that which is now 

 called the " Silurian basin," as circumscribed by gneiss, has a major 

 axis of 120 miles long from Langesund, on the S.S.W., to the Lake 

 Miosen, on the N.N.E. He will further observe, that the northern 

 and southern portions of this region, particularly the latter, have been 

 occupied by vast masses of those eruptive rocks (whether grouped 

 as granites or porphyries) which have been emitted subsequently to 

 the formation of the Old Red Sandstone. Hence it is, that in the 

 parallel of Christiania only is there to be seen a full and symmetrical 

 development of all the Silurian strata ; the eruptive rocks merely 

 showing themselves in that district as dykes and bosses of protrusion, 

 or partial superjacent sheets. 



