I860.] KIRKBT PERMIAN FOSSILS. 413 



strengthened by the acquisition of a full suite of specimens. Not 

 to rely solely upon my own judgment, however, I have submitted 

 some of the finest examples to the inspection of Messrs. R. Howse, 

 A. Hancock, and T. Davidson, who quite agree in referring them to 

 L. Credneri. 



There is no essential difference between the Permian and Carbo- 

 niferous specimens. The form of both is nearly oval. Each show 

 similar slight modifications of outline — occasionally becoming some- 

 what oblong, and having the posterior end more acuminate. The 

 lines of increment are alike in both ; and there is no difference in 

 the thickness of the shell, which in both cases is extremely delicate. 

 The Carboniferous specimens have the median elevation more promi- 

 nent than those from the marl-slate ; but in this respect they only 

 approach more closely to the Permian examples from the Kupfcr- 

 Schiefer, the German equivalent of the Marl-slate. In no respect 

 do the Permian differ from the Carboniferous specimens more widely 

 than do individuals of the same series from each other. 



The intervening space between the Marl-slate and the Lingula- 

 shale at Pyhope is G80 feet : 96 feet of this is occupied by the Poth- 

 liegende, or Lower Ped Sandstone, which, with Murchison and others, 

 I consider to be Permian* ; the rest is true Coal-measures, and in- 

 cludes seventy-one changes of strata. The predominating mineral 

 character of the latter is argillaceous ; the arenaceous and carbona- 

 ceous beds occupy less than a third of the whole. Twelve seams of 

 coal arc included in these strata, the most being unworkable ; they 

 give an aggregate thickness of 8 feet 2 inches. With one exception, 

 these coal-scams appear to have resulted from growth on the spot ; 

 for in eleven instances they rest upon " thill " — a term of the 

 Durham miners for the undcrclays containing Stigmarice, which are 

 now generally supposed to have been the soils of the Carboniferous 

 forests. In one instance a scam, 13 inches thick, rests upon a white 

 sandstone, in which case the coal ma}' be the result of vegetable 

 driftt. These facts seem to indicate that, even as a Carboniferous 

 species, Lbigula Credneri enjoyed a range in time of no mean length ; 



* Some geologists refer the Rothlicgende, or Lower Red Sandstone, to the 

 Coal-measures. Mr. Howse quotes its eonformahiliiy to. and the identity of its 

 fossils wit li t) lose of the Coal-measures as sullieient e\ idenee fop classing it wit It the 



latter strata. On the other hand. II i< contended bj sir Roderick Murchison 

 that a more comprehensive view leads to the conclusion thai it belongs to tho 

 Permian group. The question is of some interest ; and I would n-i\-r those who 

 wish for further information to Mr. Eowse'e paper in 'Annals and Mag, Nat. 

 Hist.' 2nd ser. vol. \i\. pp. -"7 & 38 : and to 'Siluria,' 2nd edit. p. '■> 17. 



t In the majority of cases, when coal rests upon sandstone, I believe this sur- 

 mise to be correct. But I have observed Stigmariaficoides, Brongn., in white 

 argillaceous sandstone, with its rootlets well preserved, and apparently in their 

 original position. In this instance the Sigiuaria may possibly have grown on 

 a Band] soil; or its roots (Stigmaria) may have penetrated through a more suit- 

 able but thin soil, into an arenaceous stratum bilow, A* a rule. nOWeVOT, il i-< 



not unlikely thai Beams of coal resting upon sandstone ma] be the result of vege- 

 table drift. 



I am informed by a friend, that in the coal-field of the Forest ofWyre, 

 nutria, with the rootlets in position, occurs in white Qne-grained sandstone, 



beneath a seam of imperfect eoal. 



