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IOWA ACADEMY OF SCIENCES. 



same questions that have so long perplexed investigators in 

 this country, are momentous problems yet not fully solved 

 in Russia. Yet, a comparison between the two widely sep- 

 arated provinces throws some light on our own perplexities. 



The basins occupied by the upper Paleozoic in Russia, and 

 the Mississippi valley, are very nearly of the same size. In 

 the first mentioned area the Permian very greatly predomi- 

 nates 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 limestone chiefly; and a 

 shallow water or littoral phase, that is coal-bearing, which is 

 best developed in the southern and western parts of the great 

 area, principally in the Donetz and Toula basins. 



COMPARISON OF GENERAL SECTIONS. 



In the consideration of a theme like the present one it is 

 recognized at the outset that comparisons of terranes of dif- 

 ferent geological provinces involve no necessary exact syn- 

 chrony, except through absolute physical means of correlation. 

 Such a standard, independent of intrinsic features of the ter- 

 ranes is not yet formulated for widely separated districts. The 

 shortcomings of the common fossil criteria, in any other than 

 the most general way and in the absence of something better, 

 are well known. Any agreement of biotic features in strati- 

 graphic successions distantly removed from one another are 



