SILURIAN ROCKS OF SWEDEN. 
14 * 
nearly the whole of a crystalline country like Cornwall 1 , in which the eruptive 
rocks constituting the chief masses have left mere remnants only of the palaeozoic 
rocks at a few places on the flanks. The knolls around Fredricksvarn are, in 
truth, quite analogous to many Cornish granitic hills which have been shown 
similarly to penetrate strata chiefly of the age of the Old Red Sandstone, &c a . 
But to return to the metamorphosed Silurian strata : w r e lastly observed, in com- 
pany with Professor Forchhammer, that at the foot of the Egeberg near Christiania, 
where the Lower Silurian alum-slate is pierced by greenstone, it is converted into 
a micac eous, quartzose, crystalline rock, to a considerable extent resembling the 
°ld gneiss of the adjacent mountain. Here, however, as in another example at 
the fortress of Christiania, and in every other case where true palaeozoic strata have 
been transmuted by igneous agency, the observer can follow the beds from the 
points of contact where they are crystalline, until receding from the disturbance, 
the strata, as they unfold, first appear as mere indurated, black and contorted 
schists, and then passing in a short space into the dark and calcareous Silurian 
shale of the bay, are overlapped by its fossiliferous limestones 3 . 
Developing elsewhere more precisely the nature of these phenomena of meta- 
1 , p} le . . 
ral ' “ ramt ' iC roc k Fredricksvarn with its zircons is a beautiful crystalline rock loaded with mine- 
including magnetic iron ore and labrador felspar, with the new species Polymenite, Jllceolite, &c. 
should ^ rea ^ n ® Ural Mountains, we shall have occasion to express a wish that distinctive terms 
from th ^ nen t0 eru Ptive rocks of age posterior to the palaeozoic strata, in order to distinguish them 
^ granites associated with gneiss. Foreign geologists naturally enough object to the use 
wor trappean as sometimes applied to the newer group, which in truth includes granites ; and as 
it ‘ ln St ’ riC *' ra ‘ n eralogical sense, as well as greenstone, occurs in the older plutonic division also, 
c ear that some term should be adopted to mark the age of the eruption of each class, since there are 
granites and syenites of different ages. We might venture to suggest for this purpose such names as 
° o-p utonic , Palceo-plutonic, &c., which, if approved, might be extended to Mezo-plutonic, &c., as more 
precisely defining the age of eruption than the terms hitherto used. In our general Map, PI. VI., all these 
^ linger granites younger than the azoic rocks are necessarily grouped under one colour and letter. In 
Map, however, of the Ural Mountains, the granites are distinguished from the greenstones and ser- 
pentines by separate marks. 
^ Since the publication of various memoirs by Professor Sedgwick and Mr. Murchison, Sir H. T. 
a Beche and Professor Phillips (including the work on palseozoic fossils of the last-mentioned author) 
'rtam fossil remains, supposed to be Silurian, have been discovered in Cornwall by Mr. Peach and other 
P ^ ons: - (See Ann. Report Roy. Geol. Soc. of Cornwall, 1844, p. 7.) 
has memoir by Mr. Murchison, containing more detailed views on the structure of Norway and Sweden, 
by P 6 f H COtmnunicate d to the Geological Society of London, in which it was shown how the able memoir 
our ° SSSOr bbrchhammer on the chemical changes from fucoid schists into gneiss-like rocks bears upon 
'lews. (See Report to the British Association for the Advancement of Science, 1844, p. 155.) 
