1845.] 603 



prevalent base in the Christiania fjord. These lowest strata are 

 surmounted by black limestones and shale, charged with fossils, 

 which leave no doubt that the inferior group represents the lower 

 Silurian rocks of the British Isles.* 



As a whole these lower Silurian rocks of Norway have very 

 little of the arenaceous character which the same group assumes 

 in certain tracts of Britain, but are most analogous to the schists 

 and calcareous flags of Llandeilo, where those masses have not 

 assumed a slaty structure. This lower division is overlaid by 

 shales and massive coralline limestones, containing many of the 

 typical species of the Wenlock limestone in the British Isles, and 

 these again by calcareous flagstones and schists, which from their 

 fossils and position may be taken to represent the Ludlow rocks. 



The Silurian strata of Norway are thus clearly divisible into an 

 upper and a lower group, with an intermediate limestone loaded 

 with Pentamerus ohlongiis, and corresponding, therefore, to the 

 Woolhope or Horderly limestone of the British Isles : but these 

 two groups constitute one inseparable and closely connected sys- 

 tem, the uppermost beds of which, composed of calcareous sand- 

 stones containing Leptczna lata, a peculiar Spirifer, and a shell 

 closely allied to Terebratula Wilsoni, are overlaid in the moun- 

 tainous tract called the Eingerigge (see annexed section), by red 



quartzose sandstone and shale that forms a deposit of great thick- 

 ness (perhaps 1000 feet), lithologically undistinguishable from the 

 old red sandstone of the British Isles. Thus the ^beds of this 

 latter group (the old red sandstone) broken through by great 

 tabular masses of porphyry, are separated from the ancient gneiss 

 on either side, and occupy a lofty tract in the centre of the 

 trough, having the Christiania fjord on the one side, and the 

 Steens fjord and Drammen on the other, both of which depressions 

 are filled with the Silurian rocks in question. 



In the Steens fjord the symmetry with which the upper Silurian 

 flagstones and tilestones rise out from beneath the great mass of 

 the old red sandstone, is very striking ; and in carrying the same 

 section across to the gneiss range on the west bank of the Drammen, 

 the upper calcareous coralline formation is separated from the 

 black Silurian flags by the same limestone, containing Pentamerus 

 oblongus, which forms the intermediate bed between the upper 

 and lower Silurians in many parts of the British Isles. But whilst 



* Among the fossils from the inferior members of the series (the lowest beds 

 of which contain fucoids) are found the genus Battus or Agnostus with Paradoxides 

 or Olenus, and in other beds Trinudeus Caractaci, Asaphus Buchii, and A. 

 tyrannus, with various Orthoceratites and other chambered shells and some 



Orthidce, including Orthis alternata and O. virgata; all forms highly charac- 

 teristic of the Lower Silurian rocks in the British Isles. With these, and 

 in still greater abundance, are found Illanus crassicauda, Asaphus expansus, and 



Choetetes petropolitanus, Orthoceratites duplex, and Sphm-onites aurantium, all of 

 which specially distinguish the Lower Silurian rocks of Sweden and Russia. 



