248 PEOCEEDINGS OF THE GEOLOGICAL SOCIEl'Y. [Mar. 8, 



Dentalium 1, Natica 2, Pleurotomaria 3, Rissoa 1, Straparolus 1, 

 Turbo 5, Turbonilla 4 : in all, 11 genera and 26 species. 



Pteeopoda. Theca 1. 



Cephalopoda. Nautilus 1. 



The whole comprises only 38 genera and 80 species. 



All of these are small and dwarfed in aspect, when compared with 

 their Carboniferous congeners, when such there are. 



In this poverty and dwarfing of the forms, these Magnesian-Lime- 

 stone fossils may also be compared with the still less numerous 

 fauna of the Caspian ; and though I am not aware that that inland 

 sea contains any Corals or Polyzoa, yet I doubt if the presence of 

 two or three species of Chcetetes (3) and Polycoelia (2), together with 

 half a dozen Polyzoa and a very small Cyathocnnus, would entitle 

 us to assume that it is impossible that they might have lived in an 

 inland salt lake, which, like the Caspian, had previously been con- 

 nected with the open ocean. 



The Magnesian-Limestone series of the east of England may possi- 

 bly, however, have been connected directly with an open sea at the 

 commencement of the deposition of these strata, whatever its subse- 

 quent history may have been ; for the fish of the Marl-slate have 

 generically strong affinities with those of Carboniferous age, some of 

 which were undoubtedly truly marine, while others certainly pene- 

 trated shallow lagoons bordered by peaty flats. But the Marl-slate 

 fish afford no certain clue to the solution of the problem as to whether 

 in our area and in other parts of Europe they inhabited open sea or 

 isolated inland salt waters. Indeed there is much to be said on the 

 other side of the question from the reptiles found by Messrs. Howse 

 and Hancock* ; for the Lepidotosaurus Duffii, which was found 

 very near the base of the limestone in marly limestone passing down 

 into Marl-slate, was a Labyrinthodont Amphibian, and Proterosaurus 

 Speneri and P. Huxleyi, from the Marl-slate, were Lacertilian 

 Reptiles. 



Besides the poverty and small size of the MoUusca, the later strata 

 of the true Magnesian Limestone seem to me to afford strong hints 

 that they may have been deposited in a great inland salt lake subject 

 to evaporation. Mr. Sorby, in a paper read before the British 

 Association in 1856, considers that the Permian dolomite was 

 chiefly " derived from comminuted and decayed calcareous organisms, 

 and subsequently altered into dolomite," and " that probably this 

 alteration was effected by the infiltration of the soluble magne- 

 sian salts of the sea- water, under conditions not yet clearly ex- 

 plained, during the period when it became so far concentrated 

 that rock-salt was frequently deposited, and that the calcareous salt 

 removed during the change had, by decomposition with the sulphates 

 of the sea-water given rise to the accumulations of gypsum." 

 Gypsum is common in the red marls of the Permian strata and in 



* " On a new Labyrinthodont Amphibian from the Magnesian Limestone of 

 Midderidge, Durham," and " On Proterosaurus Speneri and P. Huxleyi from the 

 Marl-slate of Midderidge, Durham," by Albany Hancock and Richard Howse 

 (Quart. Journ. Geol. Soc. 1870, vol. xxyi. pp. 556 & 665). 



