IOWA ACADEMY OF SCIENCES. 



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known to the trade, together with the first references to 

 the introduction of their names into scientific literature. 

 In this sense their enumeration is as geological titles. 



The general geological section of the Carboniferous of 

 the Western Interior coal field is about as follows, the 

 middle three series constituting what is commonly called 

 the coal measures: 



The terranes being the stratigraphical units, are the main 

 sub-divisions to be regarded in the present connection. All 

 appear to be more or less well defined throughout the ser- 

 ies in which they occur. Over a greater part of the area, 

 the more resistant members — the limestones— form usually 

 prominent topographic features. In this role they appear 

 as conspicuous ridges or eastward facing escarpments, run- 

 ning with many minor sinuosities nearly parallel to one 

 another and separated from each other by lowlands which 

 are worn out on the softer shales. In consequence, the 

 individual layers of the latter are usually so covered with 

 talus and other rock waste, and so easily weathered and 



