12 
NORWEGIAN SUCCESSION FROM LOWER TO UPPER SILURIAN. 
former visible in some tracts only, as at Vigersund on the Drammen, the latter 
being the well-known fucoid alum shale of the country and forming the prevalent 
base in the Christiania fiord. These lowest strata are surmounted by black lime- 
stones and shale charged with fossils, which leave no doubt that the inferior 
group represents the Lower Silurian rocks of the British Isles. 
Amid a profusion of Trilobites, some of which are of new species and have been 
named, but not figured by Dr. Boeck 1 , we find in the inferior member of the series 
(the lowest beds of which contain fucoids), the genera Battus or Agnostus (with 
Paradoxides or Olenus) ; and in other beds Trinucleus Caractaci, Asaphus Buchii 
and A. tyrannus, with various Orthoceratites and other chambered shells, and some 
Orthidse, including the O. alternata and O. virgata ; all forms highly characteristic 
of the Lower Silurian rocks in the British Isles. With the latter are associated 
and in still greater abundance, the Illcenus crassicauda 2 , Asaphus expansus and Clue- 
let es (Favositcs)Petropolitanus, Orthoceratites duplex, and certain remarkable cir- 
cular bodies related to Crinoidea, the Sphceronites aurantium, all of which specially 
distinguish the Lower Silurian rocks of Sweden and Russia. As a whole, these 
1 Of the forty-eight species of Trilobites (exclusive of a Battus) enumerated by Dr. Boeck, many of 
them, it must be stated, are named from mere fragments, which circumstance, skilful naturalist as he is, 
render the number of true and distinct species doubtful. Without distinguishing the genera (and we 
agree with him that many of the generic distinctions hitherto proposed are obscure and evanescent), he 
ranges, however, certain forms around common types. Judging from his own description and the fossils 
we examined in the museum of Christiania, we should say, that his species, Trilobites el/ipticus and 
T. elegans, are what we should call varieties of Culymene macrophthalma and C. variolaris, which with 
Asaphus caudatus, T. semilunaris (Esmlc.), Cahjmene Blumenbachii and its varieties are characteristic of the 
Upper Silurian strata which are seen in the Isles of Malmoe and Malmoe-kalv, Long Oen, Holmestrand, 
&c. All the other Trilobites cited by Boeck, of which the Illcenus crassicauda is by far the most abun- 
dant, belong to the Lower Silurian group, wherein also occur the Asaphus expansus, four species of Tri- 
nuclei, and the forms which range round Asaphus Buchii and A. tyrannus, similar, indeed, to varieties with 
which we are perfectly familiar in Wales ; together with several published Swedish species of Dalman, 
Wahlenberg, &c. (see Gsea Norvcgica, 1 Lief. p. 138.) 
2 It appears that the Illcenus perovalis of the Silurian system (drawn from an imperfect specimen) 
is identical with the I. crassicauda. This species has been found in the Lower Silurian rocks of Wales, 
since Mr. Murchison’s work was written, by Mr. Sharpe, Prof. Sedgwick, and the officers of the Ordnance 
Geological Survey. The coral Chcetetes ( Fuvosites ) Petropolitanus, so very characteristic of the Lower 
Silurian of Russia, has also been detected by Prof. Sedgwick in the older strata of North Wales. Phis 
and other facts, showing the identity between the Silurian system of Great Britain and Scandinavia, have 
been made known for the first time by comparing the fossils we brought back from Norway, Sweden and 
Russia, with those collected by Professor Sedgwick and described by MM. Sowerby and Salter (see Table, 
Journal of the Geol. Soc. vol. i. facing p. 20). The other results of the comparison of other species 
brought by us from Scandinavia, with the Upper Silurian British types, will be spoken of in the sequel. 
