642 NORTH AMERICAN INDEX FOSSILS. 



In Missouri and Iowa, the coal measures rest disconformably 

 upon the Mississippic, and are divisible into the Des Moinian, or 

 lower coal measures, and the Missourian or upper coal measures. 

 At the base in Missouri lies the Jordan coal the age of which 

 corresponds approximately to the Kittanning (or somewhat 

 higher). Of the same age or somewhat older is the well known 

 Morris coal of Mazon Creek, Illinois. Several marine horizons 

 are found in this series as, for example, the fossiliferous shales 

 and limestones (92 ft.) forming the top of the Des Moinian of 

 Iowa, and the Bethany limestone at the base of the Missourian 

 in the same field. The Plattsburg limestone, about 300 ft. above 

 the base of the Missourian, is one of a number of marine horizons 

 in the coal measures of Missouri. 



In Arkansas and Oklahoma^* a deeper coal horizon (Arkansan) 

 is interpolated between the Des Moinian and Mississippic. This in 

 part corresponds to the Pottsvillan and Kanawhan of the Appa- 

 lachian region. The succession is as follows : 



Seminole conglomerate 50 ft. 



Holdenville shale 260 ft. 



Wewoka formation 700 ft. 



Wetumka shale 120 ft. 



Calvin sandstone 145-240 ft. 



Senora formation 140-485 ft. 



Stuart shale 90-280 ft. 



Thurman sandstone 80-260 ft. 



Boggy shale, limestone and coal 2,000-2,600 ft. 



Savanna sandstone 1,000 ft. 



McAlester shale and coals 1,800-2,000 ft. 



Hartshorne sandstone 150 ft. 



Atoka shales and sandstones 3Joo ft. 



Wapanucka limestone 100 ft. 



Caney shale (in part Mississippic). 



Near the base of the McAlester shales occurs the Grady, Atoka or 

 Hartshorn coal, and about 250 ft. below their top, the Lehigh coal; 

 700 ft. below the top occurs the McAlester coal, and 50 ft. below it, 

 a fossiliferous iron ore with a marine fauna of Des Moinian char- 

 acter. Marine fossils also occur in the roof shales of the Harts- 

 horn, McAlester, and Lehigh coals, as well as in the shales above 

 the latter. All these faunas have Des Moinian affinities. In the 

 Wapanucka limestone the fossils are of an earlier (older) age, 



^ Coalgate Folio. Oklahoma geologists correlate the Calvin sandstone with • 

 the P'ort Scott limestone of Kansas. 



