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PKOCEEDINGS OF THE GEOLOGICAX SOCIETY. 



[Mar. 6, 



they were affected differently and attained their maximiim depths 

 at widely different periods *. Granting the former, the comparison 

 we have instituted with the Lancashire fauna is attended with some 

 degree of interest ; for it then relates to a group of species of contem- 

 poraneous existence with that of the Lower Limestone, as in the case 

 of the Compact-limestone group. 



I am aware that Prof. King has incidentally suggested that these 

 beds may possibly belong to the highest portion of the Permian 

 series. But, except the weight of his opinion (for which I make 

 every allowance), I see no fact that supports such a view. And 

 besides the argument already offered in favour of a different classi- 

 fication, there is the fact that four of the species ( G. antiqua, B.LeigJii, 

 N. minima, and T. Binneyi) never occur in the higher beds of the 

 Permian series in other parts of England. This might not be of 

 much consequence were the distribution of species at all variable in 

 the upper beds, so that we might expect to meet with species spe- 

 cially characteristic of certain localities ; but there is so great a 

 uniformity of distribution in the highest beds of the series — the very 

 reverse of that in the lowest — that the occurrence of species hitherto 

 found only in the inferior strata in beds of uncertain horizons would 

 certainly favour their classification with the lower rather than the 

 upper members of the series. 



§ VIII. Permian Fossihof Ireland. — Butthegroup of Permian species 

 to which the fauna of the Lower Limestone approaches most closely is 

 that occurring in the magnesian limestone of Cultra and Tullyconnell 

 in Ireland, described by Prof. Kingf. This group consists of 11 

 species; and all of them with one exception (Cy there Tyronica) are 

 common to the Yorkshire fauna. Among the Mollusca are the com- 

 mon forms of the Yorkshire deposit, as Gerv. antiqua, Ax. dubius,Myo. 

 costata, Myal. Hausmanni, T. helicinus, Bis. LeigM, and Tur. Alten- 

 burgensis ; and among the other species there are also Sten. Mackroihi, 

 Hi. dubius, and Mil. jousilla. The two assemblages have very much 

 in common, the principal differences being deficiencies. In both 

 instances Conchifers and Gasteropods are the characteristic Mollusks ; 

 and in both, these classes are pretty equally balanced. The all but 

 absence of Brachiopoda in the one, and their absence in the other, is 

 another point of agreement ; and the representation of Polyzoa, Fo- 

 raminifera, and Entomostraea by species either identical or closely 

 related completes the similitude. 



And it is quite possible, in my opinion, that this Irish group of 

 species may likewise have been of contemporaneous existence with 

 the fauna with which I am comparing it. The horizon of the Cultra 

 and Tullyconnell beds is certainly considered to be high in the series 

 by Prof. King, though, with deference to the Professor's opinion, I 

 would again suggest the possibility of a more appropriate classifica- 



* I here argue on the usual assumption of calcareous beds being the deposition 

 of deeper sea than those of an argillaceous and arenaceous nature. That there 

 are exceptions to this it would be useless to dispute ; but as a general rule it pro- 

 bably holds good. 



t 'Journ. Geol. Soc. of Dublin, vol. vii. p. 73-78. 



