In many instances, the Permian rocks are seen to repose unconformably upon the underlying Carboniferous, from which they can in addition be readily separated by their lithological characters.  In other instances, however, the Coal-measures terminate upwards in red rocks, not distinguishable by their mineral characters from the Permian; and in other cases no physical discordance between the Carboniferous and Permian strata can be detected.  As a general rule, also, the Permian rocks appear to pass upwards conformably into the Trias.  The division, therefore, between the Permian and Triassic rocks, and consequently between the Palaeozoic and Mesozoic series, is not founded upon any conspicuous or universal physical break, but upon the difference in life which is observed in comparing the marine animals of the Carboniferous and Permian with those of the Trias.  It is to be observed, however, 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 Carboniferous 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 consist 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 development, of laminated marls, or “marl-slate,” surmounted by beds of magnesian limestone (the “Zechstein” of the German 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 the Magnesian Limestone.

3.  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 developed in Kansas.  Their exact limits have not as yet been made out, and their total thickness is not more than a few hundred feet.  They consist of sandstones, conglomerates, limestones, marls, and beds of gypsum.