1855.] MURCHISON — CHRISTIANIA. 163 



respecting the Silurian formations of Christiania, and to procure a 

 competent survey and admeasurement of them. Whilst Mr. D. Forbes 

 will give you his own views on the crystalline rocks, I have to thank 

 him for having obtained from his friend M. Theodor Kjerulf the 

 map which is herewith exhibited. On it are delineated the bound- 

 aries of the Lower and Upper members of what M. Kjerulf terms 

 the "Silurian Basin of Christiania," and of the overlying Devonian ; 

 the dips of the strata being generally noted. M. Kjerulf has also 

 furnished some data to Mr. D. Forbes, among which the following 

 are important : — 



Feet. 

 The Lower Silurian schists and limestones have a thickness of . 860 

 The Upper Silurian limestones and flagstones 150 



Total thickness 1010 



In various publications, and specially in my last work *Siluria,' 

 I have adverted to the phsenomenon, that, notwithstanding the thin- 

 ness of the Scandinavian strata of this age, they exhibit as complete a 

 " natural system " as in countries where they are expanded to many 

 thousand feet of vertical dimensions. Thus, above the bottom beds 

 (often only a few feet thick) of fucoid-sandstone resting upon 

 gneiss or older granite, we meet with the so-called Alum-slates, 

 recently illustrated by the publication of their fossils by Angelin, 

 some of the forms of which were known long ago to Hisinger 

 and the older Swedish naturalists. Whether at Andrarum or other 

 places in Scania where I have examined it, or on the flanks of the 

 Norwegian trough under consideration, this zone of schist has nowhere 

 a greater thickness than from 60 to 80 feet, whilst its equivalent in 

 Wales (the Lingula-flags) has a thickness of many thousand feet, as 

 assigned to it by the British Government Surveyors, who place it as 

 the bottom rock of the Silurian System. Still, notwithstanding this 

 vast disproportion in dimensions, the thin shred of Scandinavia has 

 afforded many more Trilobites of the genera Paradoxides, Battus^ 

 and Olenus, than the grand British mass. In consequence of its 

 fauna, M. Barrande has recognized the Alum-slate of Scandinavia as 

 being the exact representative of his primordial Silurian zone of 

 Bohemia. 



Then, in the succeeding few hundred feet of black schists, with 

 occasional courses of limestone, which constitute the chief body of 

 the Lower Silurian rocks, we have just the same profusion of typical 

 fossils, whether they be Asaphi, Illceni, Trinuclei, or simple-plaited 

 OrthidcBy as in the capacious mountain escarpments of Wales and 

 Siluria ! 



lu parts of Scandinavia, and particularly near Christiania, a lime- 

 stone charged with the Pentamerus oblongus is, as in other parts of 

 Europe (as well as in America), the band which separates the Lower 

 from the Upper Silurian, and which, according to the predominance of 

 fossils of the one or the other, may locally be classed with either group. 



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