366 Termination of the Paleozoic Period, 
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analogous in structure to the Fenestella, Retepora and Gorgonia. 
But these reticulated corallines are by no means confined to the 
palzozoic strata. Six species of Retepora are given by Goldfuss, 
as occurring in the eretaceous system of Maestricht, and two 
species in particular, viz: R. fenestrata, Goldf., and &. vibieata, 
Goldf., are remarkably analogous in structure to forms occurring 
in the Silurian and Devonian rocks, whilst the genus Gorgonia 
is still living in the ocean. 
As yet but one single species has been established as common 
to the Silurian, Devonian, Carboniferous and Permian systems, 
viz: Chonetes sarcinulata, (O. striatella, Dal. L. lata, v. B.;) 
since the Sirifer hystericus is given in the tables as only prob- 
lematical in the Permian system, and but one, besides the pre- 
ceding, iscommon to the Permian and Devonian, viz: Terebra- 
tula concentrica. s 
The only other four species of brachiopods noted in the table 
above referred to, not peculiar to the Permian system, are—Lin- 
ula mytiloides, Productus Cancrini, Spirifer cristatus, Terebra- 
ossyi. These are given as common to the Permian and 
Carboniferous systems. 
It appears from the above, that the force of the argument in 
favor of placing the Permian system in the paleozoic period, 
proves chiefly an analogy between it and the Carboniferous sys- 
tem; for when we examine the evidence to show that the Devo- 
nian and Silurian systems belong to the same era, the proof Is 
feeble, resting on but two instances of specific identit 
Reflecting on the above, and other facts which are about to be 
enumerated, I have been led to differ from the writers alluded to, 
or at least to doubt the propriety of a classification which throws 
the Permian and Carboniferous systems into the paleeozoic pe- 
riod, high as the authority is from which the proposed classifica- 
tion emanated. 
fore proceeding to give the arguments in favor of a different 
arrangement, let us see what ought to be our most important guide 
in determining the great division of rocks. 
ese divisions are, in one sense, arbitrary. Geological eras 
cannot be considered as separated by abrupt transitions: W 
the series are complete, there is a blending of one system into the 
other; especially a gradual dying off of orders, genera and spe- 
cies of fossil forms, rendering it difficult, sometimes impossible, to 
w broad and well defined linés of separation. Still, taken as 
a whole, the best guides in defining their limits seem to be the 
evidence of a more or less complete change in the physical con- 
dition of our planet; the termination of one great class of phe- 
nomena and the beginning of another; the extinction of races an) 
the development, of new tribes; the proofs of the elevation and 
disruption of formations and the unconformability of s 
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