806 



SIR J. W. DATVSON ON THE EOZOIC AXD PALJEOZOTC 



Olenellus, Solenopleura, Hyolitlies &c. in the conglomerates of tlie 

 Quebec group*, and it also appears in the Georgia series of Yermont t, 

 nd, according to Walcott, as far west as iJs^evada and Utah J. On 

 the other hand the upper members of the Cambrian, the Dikeloce- 

 j>halus-gTO\\p or Potsdam Sandstone, is apparently altogether absent 

 n the Acadian provinces, which at that time must have been under 

 ocean-depths in which deposits of a verj' different kind would be 

 produced, or elevated into land, perhaps the border of an Atlantic 

 island now mostly submerged. It seems doubtful if any good equiv- 

 alent of the Potsdam exists in England or Wales. 



It is otherwise, however, with the next succeeding formation, that 

 passage-series between the Cambrian and Ordovician known in "Wales 

 as the Tremadoc. This, in America, takes a more inland position, 

 and becomes an interior or submarginal formation connected with 

 the Quebec group to be mentioned in the sequel. At ]y!atane and 

 Cape Eosier, as noted by me in 1883 §, and as Lapworth has more 

 fuUy proved in 1886 H, we have a true Tremadoc filled with Dic- 

 tyonema sociale aud containing also fragments of characteristic 

 TriLobites. Further inland, on the main American plateau, these 

 beds are not found, but are represented by the peculiar " Calciferous " 

 formation, a dolomite formed apparently in an inland sea and having 

 a characteristic fauna of its own. 



A very remarkable and exceptional feature in British geology is 

 the appearance in the sandstone and limestone of the Durness 

 series of Scotland of a group of fossils long ago recognized by Salter 

 as of the interior American type %. In other words there existed in 

 Scotland, within the shelter of the old Laurentian and Huronian 

 ridges, an area which sustained a fauna similar to that of the internal 

 plateau of America, and which, so far as known, did not exist in 

 Wales or on the American coast. This curious case of apparent isola- 

 tion we might better understand did we know the exact geographical 

 arrangements of the period. One consideration bearing on it is the 

 probability that the Trilobitic and Grraptolitic faunas of the coast 

 mainly belonged to cold northern currents, while the Plateau-faunas, 

 richer in Cephalopods, Gasteropods, and Corals, belonged to the 

 superficial warm currents passing over shallow plateaus, or to the 

 tepid waters accumulated in closed basins. This is, I think, quite 

 manifestly the case with the very dissimilar marginal and continental 

 faunas to be noticed under the next heading. Salter seemed to sup- 

 pose that the occurrence of these fossils in Scotland, and not to the 

 south, indicated a dim atal difference. In this he was justified; but 

 the character of the climate was probably different from that which 

 he imagined. 



* At Metis, St. Simon, &c. 



t Emmons's ' American Geology ;' BilHngs's ' PalaBOzoic Fossils.' 



I BuUetin U. S. Survey. 



§ Eeport Peter Eedpath Museum, No. ii. Eickardson's observations at 

 Matane. 



II Transactions Eoyal Society of Canada. 



*[ Quart. Journ. G-eol. Soc. vol. xv. These rocks are also recognized by GeiMe 

 in Skj-e (Quart. Journ. Geol. Soc, Feb. 1888). 



