368 PEOCEEDINGS OE THE GEOLOGICAL SOCIETY. [Mar. 7, 



loped set of tlie marine Devonian rocks are covered by anything 

 like a complete series of Carboniferous Limestone. Where the two 

 things are present, as near Cork, they are neither of them so com- 

 plete as in adjacent areas where only one is found. 



But by the hypothesis which I now propose, the place of these 

 marine Devonian beds will be fixed stratigraphically between the top 

 of the Old Red Sandstone and the base of the Coal-measures, in 

 North Devon as in Ireland. 



I cannot yet speak from personal examination of South Devon, 

 but, from the descriptions of Sedgwick and Murchison and others, 

 it appears to have a more complicated structure than JN'orth Devon. 

 The occurrence of red sandstones above the Plymouth limestones 

 (Trans. Geol. Soc. vol. v. p. 657) might at first appear to place those 

 limestones below the Old Eed Sandstone. On this point I may, 

 by way of caution, refer to the previous remarks at p. 323, that it 

 is not every group of red sandstones, with some beds even of Car- 

 boniferous Limestone immediately over them, that is entitled to 

 be called Old Red Sandstone. We have in Ireland beds of red 

 and yellow sandstones and conglomerates in the Carboniferous Lime- 

 stone ; there is no reason, therefore, why similar beds may not oc- 

 cur in the Devonian beds of Devonshire. In neither case should 

 these red sandstones be identified with the Old Red Sandstone 

 proper. 



The true Old Red Sandstone is the conformable base of the great 

 Carboniferous series, and contains no marine fossils ; the Devonian 

 beds proper (those containing marine fossils) lie above it, side by 

 side with the Carboniferous Limestone, both being directly covered 

 by the Coal-measures. 



The difierence in the fossils of the Carboniferous Limestone and 

 the Devonian beds must then be held to be the result of space 

 rather than of time, and to mark the influence of nature of bottom 

 and difference of province, rather than of chronological periods. 



This difi'erence will be somewhat analogous to that observable in 

 the case of the Upper Silurian rocks of North Wales and of Siluria 

 proper. The Wenlock rocks of Denbighshire abound with impres- 

 sions of the various species of Theca (Q. J. G. S. vol. ii. pi. 13), 

 so that they might well be called Theca flagstones ; but this fossil 

 is either entirely absent from the Wenlock rocks of Siluria proper *, or 

 very rare in them, while the common Wenlock fossils are rare in 

 Denbighshire. 



The difference noted by M. Barrande between the Trilobites in 

 the contemporaneous Silurian beds of Bohemia and Scandina^da will 

 occur to every geologist as a still more striking instance. 



The influence of geographical distribution, which is so obvious on 

 the existing species of animals and plants, has hardly yet, I think, 

 been sufficiently allowed for by palaeontologists. As we trace forma- 

 tions through different countries, we must hold ourselves prepared 

 to find the same species in beds not strictly contemporaneous, and 



•^ Theca ancejos is mentioned by Mr. Salter as found near Eastnor Castle, 

 Malvern Hills. Mems. Greol. Sury. vol. ii. p. 855. 



