332 



C. /?. KEYES 



are remarkably alike. The basins occupied by these rocks are very 

 nearly of the same size. As already stated in the first-mentioned 

 area, the Permian very greatly predominates as the surface rock. 

 In the last-named, the coal measures. The Carboniferous of 

 Russia presents two very distinct aspects — a thalassic facies, 

 occurring on the western flanks of the Urals, and made up of 

 limestones chiefly ; and a shallow water or littoral phase, that is 

 coal bearing, and that is best developed in the southern and 

 western parts of the great area, principally in the Donetz and 

 Toula basins. 



COMPARISON OF GENERAL SECTIONS 



