1857.] MURCHISON SILURIAN ROCKS OF SCANDINAVIA. 37 



to me descriptive letters, with illustrative diagrams, exactly defining the 

 relations and dimensions of the different rock-masses, as well as the 

 organic remains of each stratum ; the most characteristic specimens 

 of the latter having been transmitted to England for comparison*. 



The same zealous author has published a work in which he clas- 

 sifies the two great -sedimentary deposits of South Norway, the one 

 exhibiting a vast development of unfossiliferous rocks, to which he 

 applies the name of Cambrian, — the other being the overlying Silu- 

 rian rocks, of which he describes each stratum with its respective 

 fossils from the Alum Shales upwards. 



My able coadjutor in the work on Russia and the Ural Moun- 

 tains, Count A. von Keyserling, had previously translated and sent 

 to me a memoir, by Prof. Schmidt, on the succession of the Silurian 

 rocks of the Russian province of Esthonia, and the adjacent isles, 

 which portrays the distinctions of the various members composing 

 the Silurian system with much greater precision and clearness than 

 had ever before been applied to that region. 



I now lay an outline of these documents before my associates, in 

 order to show them how independent observers in other tracts have 

 come to the conclusion, that the Silurian system, as defined by them, 

 as well as by myself, forms a natural-history group, whether we look 

 to its geological relations, or its zoological contents. In the sequel 

 I will revert to my own comparison, and point out how the Silurian 

 rocks of Scandinavia and Russia agree with those of our own country, 

 from the lowest to the highest beds inclusive. 



Norway. — To begin with Norway, M. Kjerulf divides the whole 

 Silurian series of his country into three physical groups, which he 

 severally names in ascending order from the tract where it is best 

 exhibited ; viz. Oslo, Oscarskal, and Malmo, and in these he recog- 

 nizes fourteen subdivisions. 



A. The Oslo group consists of a base of sandstone and conglome- 

 rate, which, though not exposed near Christiania, occur at Lango, 

 Mjosen, and other places. This bottom rock (1), which is unfossili- 

 ferous, is followed by alum-schists and bituminous limestone (2) ; 

 Lower graptolite-schists (3) ; Orthoceratite-limestone (4) ; and 

 Upper graptolite-schist (5). 



B. The second or Oscarskal group is composed of calcareous and 

 argillaceous flags (6 & 7) ; with intermediate orthoceratite-limestone 

 with encrinite-schists and calcareous sandstone (8). 



C. The Malmo or upper group exhibits at its base argillaceous 

 schists (9 a ) with calcareous flags (9 b ), and Pentamer us -limestone (9 C ) 

 Coral-limestone, often concretionary (10); Encrinite-shale (11) 

 Upper orthoceratite-limestone (12); Upper graptolite-schist (13) 

 Upper Malmo limestone and schist (14). 



The following Table and the annexed general section, fig. 1, explain 

 this order. 



* These are now placed in the Museum of Practical Geology, 



