412 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Mar. 14, 



March 14, 1860. 



The Rev. T. G. Bonney, M.A., Fellow of St. John's College, Cam- 

 bridge, and the Rev. Henry Eley, M.A., Broomfield Vicarage, Chelms- 

 ford, were elected Fellows. 



The following communications were read : — 



1. On the occurrence of LrNGULA Credneri, Geinitz, in the Coal- 

 measures of Durham ; and on the Claim of the Permian Rocks to 

 be entitled a System. By J. "W. Kirkby, Esq. 



[Communicated by T. Davidson, Esq., E.G.S.] 



The recurrence of Carboniferous species in Permian strata is not new 

 to palaeontologists ; for recurrent species from the Carboniferous 

 fauna, and such as were supposed to be recurrent, have been noticed 

 by several observers. Messrs. Lonsdale*, Jones t, Howse t, King§, 

 and Davidson ||, as well as others, have identified Permian with Car- 

 boniferous species, or vice versa, though it may be remarked that in 

 some cases their determinations have been undoubtedly erroneous. 



The discovery of another species which had long been thought 

 characteristic of the Permian period, in Carboniferous strata, is there- 

 fore not so novel a fact as might appear at first sight. At the same 

 time, I deem it well to record its occurrence, which is not without 

 importance. It is of interest merely as the discovery of another 

 species which is common to the faunae of the two later palaeozoic eras; 

 and it is of consequence as a fact which assists in illustrating some 

 of the physical conditions which prevailed during the deposition of 

 the Upper Coal-measures of the North of England. 



In the Permian formation, Lingida Credneri is confined to the 

 lower strata. In England it is restricted to the " Marl-slate," and 

 the lower beds of the " Compact Limestone. It is not common in 

 these members, having been found only at Ferry Hill, Thrislington, 

 and Thickley. 



As a Carboniferous shell it only occurred to me during the summer 

 of last year (1858), at the Ryhope Winning, near Sunderland. I 

 first observed it in a thin bed of dark shale, at a depth of 951 feet 

 from the surface, or 592 feet from the base of the overlying Permian 

 strata. In this bed it was exceedingly rare ; but I found it more 

 plentiful in a thick stratum of grey shale just above the bed already 

 mentioned. 



From the first I was struck with the resemblance of these Lin- 

 gular to the Permian species L. Credneri ; and my opinion was only 



* Lonsdale on Corals, in ' Silurian System ' (Fenestella antiqua). 



t Jones on Entomostraca, in Prof. King's Mon. Perm. Eoss. pp. 61, 62 ( Cythere 

 [Bairdid] curta, &c). 



J Cat. of Fossils in Perm. Syst. of Northumb. and Durh. p. 40 (Spirorhis glo- 

 bosics). 



§ Cat. Org. Rem. of Perm. Syst. p. 13 (Loxonema rugifera) ; see also Mon. 

 Perm. Eoss. p. 150 (Terebratida sufflcda). 



|| Mon. Carb. Brachiopoda, pp. 14, 38j& 58 (Terebratula Sacculus, &c.) ; also 

 in ' Geologist,' vol. iii. pp. 19 & 21. 



