194 HISTORICAL PALAZZONTOLOGY. 
Trias. The division, therefore, between the Permian and Tni- 
assic rocks, and consequently between the Paleozoic and Me- 
sozoic series, is not founded upon any conspicuous or universal 
physical break, but upon the difference in life which is ob- 
served in comparing the marine animals of the Carboniferous 
and Permian with those of the Trias. It is to be observed, how- 
ever, that this difference can be solely due to the fact that the 
Magnesian Limestone of the Permian series presents us with 
only a small, and not a typical, portion of the marine deposits 
which must have been accumulated in some area at present 
unknown to us during the period which elapsed between the 
formation of the great marine limestones of the Lower Carbon- 
iferous and the open-sea and likewise calcareous sediments of 
the Middle Trias. 
The Permian rocks exhibit their most typical features in 
Russia and Germany, though they are very well developed in 
parts of Britain, and they occur in North America. When 
well developed, they exhibit three main divisions : a lower set 
of sandstones, a middle group, generally calcareous, and an 
upper series of sandstones, constituting respectively the Lower, 
Middle, and Upper Permians. 
In Russia, Germany, and Britain, the Permian rocks con- 
sist of the following members :— 
1. The Lower Permians, consisting mainly of a great series 
of sandstones, of different colours, but usually red. The base 
of this series is often constituted by massive breccias with 
included fragments of the older rocks, upon which they may 
happen to repose ; and similar breccias sometimes occur in 
the upper portion of the series as well. The thickness of this 
group varies a good deal, but may amount to 3000 or 4000 
feet. 
2. The Middle Permians, consisting, in their typical de- 
velopment, of laminated marls, or ‘ marl-slate,’ surmounted 
by beds of magnesian limestone (the ‘‘ Zechstein”’ of the Ger- 
man geologists). Sometimes the limestones are degenerate or 
wholly deficient, and the series may consist of sandy shales 
and gypsiferous clays. The magnesian limestone, however, of 
the Middle Permians is, as a rule, so well marked a feature 
that it was long spoken of as #AZe Magnesian Limestone. 
a The Upper Permians, consisting of a series of sandstones 
and shales, or of red or mottled marls, often gypsiferous, and 
sometimes including beds of limestone. 
In North America, the Permian rocks appear to be confined 
to the region west of the Mississippi, being especially well de- 
veloped in Kansas. Their exact limits have not as yet been 
