12 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 3, 



land of Sweden, in which these rocks occur (with the exception 

 oF Scania), Lower Silurian rocks only are visible, and the strata 

 which I refer to the Old red sandstone seem, in all these tracts, to 

 have been deposited next in succession without the intervention of 

 the Upper Silurian strata. 



The red sandstone in question is separated from the Silurian 

 rocks by a rugged range of porphyry covered with dense woods, 

 whose sides are so loaded with debris, that in a few situations only 

 is the solid rock visible. Of the forty to fifty varieties of por- 

 phyries and crystalline rocks (including syenite, syenitic granite, 

 serpentine, &c.) which are worked into ornaments and polished at 

 the works of Elf Dal which we visited, but three or four are taken 

 from rocks in situ. These quarries afford the dark and purple 

 porphyries which are so well known over Europe, and of which 

 beautiful monuments occur in the Royal Gardens and public places 

 of Stockholm. We ascended from the valley of the Elf river through 

 heaps of porpliyritic detritus, to visit the quarries of Bliberg, which 

 are opened on the southern face of the summit of hills, whose 

 outlines are formed of domes, rising to 700 or 800 feet above the 

 sea. At Bliberg, the porphyry, which is cut down vertically to a 

 depth of about thirty feet, and horizontally for about 100, has a 

 dark purple base filled with small crystals of white felspar, and is 

 traversed by vertical joints, the faces of which strike 10° east of 

 north: these joints are cut by rectangular planes (the beds of the 

 quarrymen) which incline very slightly (5°) to the north. Though 

 the rock is of exceedingly uniform composition at this spot, the 

 very same range of hills a little to the west contains a light red and 

 different porphyry, whilst to the east, at only a very short distance 

 from Bliberg, it passes into the syenite or granitello of Garberg*. 



Thus, in the ridges of the Elf Dal, as in the great dome-shaped 

 mass between the Siljan, Orsa and Skatunge lakes before described, 

 one portion of the same rocks (all erupted posterior to the palaeo- 

 zoic age) is a porphyry, and another a granite. This fact is, indeed, 

 completely in harmony w^ith Avhat was specially alluded to in my 

 memoir on the environs of Christiania, where various kinds of por-' ! 

 phyryt, syenite, granite and greenstone, all integral parts of the same 



* It is from this rock that the Swedes are now cutting the mouument to be 

 erected at Stockholm to the memory of Charles XIV. ; v 



t By a letter recently received from my distinguished friend Leopold von Buch, 

 I learn that after a careful analysis, M. Gustaf Rose has determined the peculiar 

 rock of Ringerigge near Christiania, with large rhombic crystals of glassy felspar 

 (the rhomb-porphyr of Von Buch), to be an augite rock. The analyses of this 

 skilful mineralogist, when added to those of Berzelius and others, may doubtless 

 ultimately define the true composition and characters of crystalline rocks, and en- 

 able us to group them more precisely than has hitherto been possible in their re- 

 spective families ; but can such nomenclature be shown to have reference to 

 geological relations, by marking distinct eruptive rocks as peculiar to particular,^ 

 ffiras of disturbance ? If certain granites, porphyries and greenstones were (as I" 

 believe) erupted at the very same time, and if in the very same ridge all these rocks^^' 

 are so collocated in reference to bedded strata that they must have been erupted'^''' 

 simultaneously or nearly so, this distinction of M. Rose, as far as I now under- 

 stand it, would seem to be rather mineralogical, than historical or geological. 



