i:n^teoduction. 



The fossils described in the following pages belong, for the most part, to a series 

 of deposits overlying the North of England Coal-measures, and passing under the 

 Midland Saliferous marls, and sandstones. These three groups of deposits represent 

 distinct consecutive geological systems ; the lowest or most ancient one representing 

 the Carboniferous ; the highest or most recent one, the Triassic ; and the intermediate 

 one, the Permian. The rocks of the Permian system were deposited during the latest 

 division of the Protozoic or Primary organic period ; and those of the Triassic, in the 

 earliest division of the Deuterozoic or Secondary period. The separation between 

 these two great periods is based on the prevailing idea, that Organic Nature underwent 

 a most marked change at the time the Permian rocks were being deposited : this may, 

 or may not have been the case ; at any rate, the prevalence of the idea invests the fossil 

 remains of the rocks in question with the utmost importance in philosophical geology. 



Although a few earlier brief notices appeared descriptive of the deposits 

 immediately connected with the province of this Monograph, it was not until the 

 Rev. Professor Sedgwick published his admirable Memoir ' On the Geological relations 

 and Internal Structure of the Magnesian Limestone/ that they became properly 

 appreciated. The edifice so ably reared for England, by one of the illustrious founders 

 of Modern Geology, has of late had its parallel erected for a far distant region, by 

 another, whose name is as inseparably connected with the early history of this 

 ennobling science. 



Investigating the Geology of Russia, Sir Roderick I. Murchison, with his colleagues 

 M. de Verneuil, and Count Keyserling, discovered in Perm, and the adjoining countries 

 on the Western or European flanks of the Ural Mountains, an extensive group of rocks, 

 consisting of Limestones, Gypseous and Saliferous marls, and repeated alternations of 

 Cupreous grits, containing numerous fossils intermediate in character between those 

 respectively belonging to the Carboniferous, and the Triassic system. At the com- 

 pletion of their investigations. Sir R. Murchison became fully convinced, that the rocks 

 in question were the exact equivalents of the Todte-liegende, Mergerl-schiefer, ar 1 

 Zechsteins of Germany ; and of the Lower New Red Sandstone, Marl-slate, and 

 Magnesian Limestones of England, — our home deposits having been previously demon- 

 strated to be of the same geological age as those just named occurring in Germany. 



The extensive development of these deposits in the Government of Perm, where they 

 occupy an area twice the size of France, — their containing a far more copious and 



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