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PHOCEEDINGS OF THE GEOLOGICAL SOCIETY. 



[Mar. 6, 



ward over the other. It is probable when we acquire a better 

 knowledge of the fossils occurring in the intervening range of 

 Permian strata in the northern half of Yorkshire, that the differ- 

 ences noticed may be found to be the result of gradual changes in 

 the distribution of species. And it is possible that still further 

 south other arrangements of species may obtain that are peculiar to 

 their own localities ; just as in the case of the two following local 

 faunae which, in all probability, had a contemporaneous existence 

 further to the west. 



It is worthy of attention that several of the Yorkshire species, 

 which were of contemporaneous existence in Germany, appeared in 

 the British area first in Yorkshire. This is the case with Chemnitzia 

 Roessleri, Dentalium Sorbyi, Turbo helicinus, Straparollus Permianus, 

 Turritella Altenburgensis, and Macrodon striatus, which did not ap- 

 pear in the Durham area until the era of the Shell-limestone. It is 

 not very evident whether in the latter case the migration was from 

 the Yorkshire region or that of Germany ; but as other species ac- 

 companied these which do not occur in the Lower Limestone of York- 

 shire, though common to the Lnter Zechstein, it may be presumed 

 that it proceeded from the latter. Indeed, when we remember that 

 the Permian fauna attained its maximum in Germany during the 

 period of the Lnter Zechstein*, and in England not until that of the 

 Shell-limestone, it seems highly probable that a general migration 

 of species — or rather of their individuals, the species still continuing 

 in the old area — took place to the westward while the middle portion 

 of the Permian series was being deposited, especially as more than 

 half of the additions to the British fauna during the Shell-limestone 

 period were Lnter Zechstein species. 



§ VII. Permian Fossils of South Yorkshire compared with those 

 of Lancashire. — There is another group of species with which it may 

 be well to institute a comparison. I refer to that belonging to the 

 Permian strata of Lancashire, whose geographical position is nearer to 

 the Yorkshire beds than that of the Compact Limestone, though 

 their vertical position in the series is not so well determined. This 

 little local fauna consists of only seven species ; three of these are 

 Gasteropods — viz. Turbo helicinus (with var. Mancuniensis), Pissoa 

 Leighi (with var. Gibsoni), and Natica minima. The rest, with the 

 exception of a Sponge (Tragos Binneyi), are Conchifers — viz. Gervillia 

 antiqua, Axinus dubius, and Myoconcha costata. Now all these 

 species, except the Sponge, occur in Yorkshire ; and all of them are 

 common species there, but the one just-named and Natica minima. 

 Two of the species we readily recognize as the most common of the 

 Yorkshire fauna. And two of the Univalves (Natica minima and 

 Eissoa Leighi) are in England only found in the Lancashire and 

 Yorkshire beds. 



Therefore making every allowance forthesmallnessof theLancashire 

 group of species, there seems to be a much more intimate relation- 

 ship between it and the Yorkshire fauna (Lower Limestone), than 



* See an excellent tabic of species occurring in the Zechstein of Germany, by 

 Baron von Schauroth, in the Zeitsch. d. Deut. geol. Gresell. 1854, pp. 569, 574. 



