185/.] MURCHISON — SILURIAN ROCKS OF SCANDINAVIA. 51 



the typical Silurian tracts of Shropshire, Herefordshire, and Radnor- 

 shire. This upper band only is the May Hill Sandstone*. 



In parts of South Wales, where both members of the Llandovery 

 rocks exist, there is usually, indeed (but in my opinion not always), a 

 transgression between them, as traced by Professor Ramsay and Mr. 

 Aveline, the lower member constituting over large areas the regular 

 capping of the Caradoc or Bala formation, the upper or May Hill 

 rock appearing to be usually the symmetrical base (as in Siluria 

 proper) of the Upper Silurian group. As, however, the same species 

 of Pentamerus, Atrypa, and Petraia, &c, occur in both these di- 

 visions, I am induced by this community of type, and by the opinion 

 of Mr. Salter, to consider the two bands as forming one natural- 

 history province which connects the fauna of the Lower and Upper 

 Silurian groups. 



Now, if we refer to certain other regions, the truthfulness of this 

 view is strikingly confirmed ; since in them we can detect no such 

 transgression or hiatus as occurs in Wales and the border-counties 

 of England. 



Even in the neighbourhood of Girvan, in Scotland, fossiliferous 

 Lower Silurian rocks of the Caradoc age seem to graduate upwards 

 conformably into the Pentamerus-zone in question, containing not 

 only the P. oblongus in profusion, but also the Atrypa hemisphcerica, 

 with the Phacops Stokesii of the Wenlock limestone ; and thus 

 leaving no doubt that we have there reached, as I formerly showed, 

 the base of the Upper Silurian rocksf. 



In Norway, however, where the area under consideration is much 

 larger, and where all the Silurian strata are clearly exposed in numerous 

 convolutions in the different islets of the Bay of Christiania, there is, 

 independently of all breaks caused by the intrusion of igneous rocks, 

 a perfectly conformable succession from the Lower to the Upper 

 Silurian^. There, as in Esthonia, the Pentamerus-zone is simply 

 the central link of an unbroken Silurian chain ; so local is the phy- 

 sical disturbance in the Welsh region seen to be, when the whole 

 surface of Northern Europe is explored. 



Whilst the Norwegian and Swedish sections are so valuable in 

 showing the base of the System, the Esthonian order of the fos- 

 siliferous strata is highly instructive hi demonstrating the accord- 

 ance of the Upper Silurian rocks with our own. The observations of 

 M. Schmidt are, indeed, most valuable in placing before us, for the 

 first time, a complete exposition of all the natural subdivisions of the 

 Silurian series of so large a part of European Russia. In Esthonia, 

 the approximation to the British succession, from the Llandeilo for- 

 mation to the summit of the Upper Silurian, is very remarkable. 



Just as in Norway, England, and America, so in Esthonia the 



* See Proc. Geol. Soc. vol. ii. p. 13; Sil. Syst. p. 442, pi. 36. f. 13; Sedgwick 

 and M'Coy, Quart. Journ. Geol. Soc. vol. ix. p. 215; and Phil. Mag. 4th Ser. 

 vol. viii. p. 301, &c. 



f Quart. Journ. Geol. Soc. vol. vii. p. 149. 



t See the diagram-section across the Territory of Christiania, Quart. Journ. 

 Geol. Soc. vol. viii. p. 182. 



E 2 



