40 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 6 



O . Jiabellulum (?), Bellerophon bilobatus, B. acutus, Orthoceras du- 

 plex, 0. annulatum, Lituites cornu-arietis, Phacops conophthalmus 

 (Powisii, Sil. Syst.) ; with many Trilobites of species peculiar to 

 Sweden, but, all belonging to the Lower Silurian genera, Asaphus, 

 Ogygia, Trinucleus, Olenus, &c. 



The group (6, 7) consisting of calcareous and argillaceous flags, in- 

 termediate orthoceratite-limestone, and lower encrinal schists, though 

 intimately connected by many forms with the underlying divisions, 

 is yet characterized by many other fossils, which enable us to refer 

 it to the true Caradoc or Bala formation, as now defined, and as will 

 be more completely explained in a new edition of ' Siluria.' These 

 fossils are, Orthis calligramma, 0. testudinaria, O. Pecten, Leptcena 

 sericea, Lingula attenuata, Bellerophon bilobatus, B. acutus, Conu- 

 laria quadrisulcata, and probably C. Sowerbyi, with other species. 

 Orthoceras duplex, O. gigas, 0. dimidiatum, O. distans, and O. annu- 

 latum ; the last three being Upper Silurian forms in Britain. The 

 other fossils of Lower Silurian age are : Lituites cornu-arietis, Tro- 

 cholites anguiformis, Euomphalus, and Turbo ; several species, in- 

 cluding Euomphalus alatus, Hisinger, with Echinosphcerites auran- 

 tium, Tentaculites anglicus (annulatus, Sil. Syst.), with the well- 

 known Trilobites Asaphus expansus, Trinucleus concentricus (Carac- 

 taci, Sil. Syst. var.), T. seticornis, Ampyx nasutus, Ogygia, Calymene 

 Blumenbachii (var. pulchella), and the Phacops macroura, Sjogren, 

 which closely resembles the P. truncato-caudatus of the British 

 Caradoc formation. The Corals are Stenopora fibrosa and its variety 

 Lycoperdon, with species of Turbinolopsis, &c. 



The calcareous sandstone (No. 8, sections) would seem, from its 

 organic remains, to constitute the commencement of a transition from 

 the Lower to the Upper Silurian rocks, such as is seen in the Lower 

 Llandovery rocks of South Wales. Thus, with the Orthis testudinaria 

 and O. zonata, Dalm., and Patella antiquissima, His., occurs a 

 characteristic Lower Llandovery species, Rhynchonella angustifrons, 

 M'Coy, and many large smooth Pentameri of species not yet named. 

 Here are some associated fossils which are also commonly found in the 

 Upper Silurian rocks of Britain. These are : Strophomena depressa, 

 Euomphalus sculptus, Phragmocerasl (Cyrtoceras) ventricosum, En- 

 crinurus punctatus, Actinocrinus moniliformis, Favosites alveolaris, 

 Heliolites megastoma, Halysites catenularius, Cyathophyllum turbi- 

 natum, &c. 



In speaking of the characters of the fossils of this zone, it is to 

 be observed, that the characteristic Lower Silurian trilobites have 

 already disappeared*. 



The argillaceous schists with calcareous flags (No. 9a) obviously 

 represent also a part of that intermediate group connecting the Lower 

 and Upper Silurian, to which I have now assigned the name of 

 " Llandovery rocks." For, in these beds certain species of Pentameri 

 are first met* with, whilst the overlying limestone (9b) is, as in 



* Several of these corals and shells in Britain range from the Llandeilo forma- 

 tion to the base of the Ludlow rocks. 



