REVIEW OF THE PERMIAN FOSSILS. 
213 
near Manchester, and in the uppermost coal-measures only ; beds, in fact, imme- 
diately subjacent to strata of the Permian age'. Whilst, therefore, fishes, con- 
sidered as a class, were propagated throughout the sera of which we are treating, 
we see in the solitary presence of this species, and in one district alone, the 
confirmation of that law generalized by the researches of Agassiz, that these ver- 
tebrata serve to mark with extreme precision the age of the deposit in which they 
are found ; there being the rarest example of any one species having lived beyond 
the duration of the waters and the peculiar sediment in which it was called into 
being. 
Above all, the Permian epoch is remarkable in being the most ancient, in which 
the labours of geologists have as yet brought to light the existence of Saurians. 
The bones of this class of large Vertebrata occur, both in beds beneath the Zech- 
stein and in the upper portion of the system, — we speak of the Thecodont Sau- 
rians, Palseosaurus and Protosaurus. This striking fact, which is in parallel, if we 
may so speak, with the annihilation of Trilobites, indicates the incessant action of 
that law of improvement and partial alteration in the animal kingdom, the effects 
of which are slow and successive, and appear to be often independent (specially so, 
indeed, in Russia) of those great physical mutations which have affected the sur- 
face of the planet. 
Having reviewed the Permian fauna as a whole, and having brought prominently 
forward the relations by which it is connected with those of the preceding period, 
it is now necessary to consider it under another point of view, and to ascertain the 
nature of the modifications which it undergoes in distant geographical regions. In 
the first instance we have followed it back in time , and have compared the whole 
fauna of the period with that which preceded it We are now called upon to study 
it in distance, or in its horizontal extension, to compare its different parts with each 
other, the fossils of Russia with those of Western Europe ; and to see whether 
zoological deductions confirm the parallelism which we establish, between the vast 
Permian basin of Russia, and the more circumscribed deposits associated wdth 
the Zechstein and Magnesian Limestone of our own countries. 
In Russia, as in all other parts of Europe, the Permian fauna is poor in its variety 
of species. The shells are for the most part found in the calcareous bands which 
occupy its lower and central divisions, constituting, like the Zechstein and Kupfer- 
schiefer of Germany, or the Magnesian Limestone of England, the great centre of 
2 F 
1 Silurian System, p. 89. 
