A review of the stratigraphy of the vast basin west of the Urals shows the relation of the five series into which the type Permian is divisible. These are correlated with the Permian deposits of South China and southwestern United States.

The limestones of the Russian platform, commonly considered Upper Carboniferous, are shown to be equivalent to the Artinsk detritals, which are generally recognized as Permian. The lower boundary of the Artinsk is shown to be not a constant stratigraphic horizon but the contact between overlapping facies.

Although no widely recognizable break has been demonstrated in the deposits of this basin from the beginning of the Upper Carboniferous into Permian time, a broad view shows that the rapid subsidence of the geosyncline over a very great area began with the incursion of the Pseudoschwagerina fauna. This beginning of a rapid evolution in the Uralian geosyncline is correlated with the regional hiatus at the base of the Wolfcamp series in America and a profound and regional break at the same horizon in the Orient. It is concluded, therefore, that the most natural lower limit of the Permian system is at the base of the Pseudoschwagerina zone, that is, at the base of the Sakmarian in the U.S.S.R., of the Wolfcamp in America, of the Chuanshan in South China, and of the Schwagerinakalk in the Carnic Alps.