176 C. R. KEYES — A DEPOSITIONAL MEASUKE OF UNCONFORMITY 



Principal coal-beartng Formations 

 extent and character 



Heretofore it has been generally conceded that the coal seams of the 

 Coal Measures are limited to no particular horizon. This is only true 

 in a very general way. Coal is found at many different stratigraphic 

 levels, but what may be termed the productive formations are few in 

 number. 



The geological maps of the region give but faint idea of the actual 

 disposition and relations of the coal seams. A consideration of the 

 mine locations gives an equally vague conception of the horizons which 

 furnish the chief fuel supplies. The general literature is so widely scat- 

 tered and the references so disconnected that little help is to be had 

 from this source. 



Considering a coal horizon as a stratigraphic plane, along which coal 

 has formed and which may be coal-yielding or not,* the extent of indi- 

 vidual workable seams is extremely variable. There is no correspond- 

 ence between thickness and areal extent. Some of the thickest beds 

 are the most limited in their geographic distribution. The Versailles 

 (Morgan county, Missouri) deposits,! which are upward of 60 feet in 

 thickness, are less than a mile across. On the other hand, some of the 

 thinner beds are found over a very wide area. The Mystic seam J of 

 southern Iowa and northern Missouri, though only about 3 feet thick, 

 extends over many hundreds of square miles. So also the Grady seam' 

 of Arkansas and Indian territory has great areal extent. § 



PRODUCTIVE COAL SERIES IN THE NORTH 



A short time ago the present coal output of each geological formation 

 in Iowa, Missouri, and Kansas was the subject of special inquiry. In 

 order to present the facts more clearly the supplies were tabulated 

 according to percentages as follows : 



Terrane Percentages of coal Production 



Missourian series : 



Atchison shales 



Platte shales 



Lawrence shales. ...» 



Parkville shales 



Thayer shales 



Des Moines series: 



Marais des Cygnes shales. 



Henrietta formation 



Cherokee shales 



Iowa. 



0.2 



10 

 15.4 



Missouri. 



0.1 

 18.5 

 81.4 



Kansas. 



6.0 

 0.13 



0.2 



0.8 



0.2 



92.5 



♦Journal of Geology, vol. ii, 1894, p. 178. 

 tEng. and Min. Jour., vol. xlix, 1900, p. 529. 

 X Iowa Geol. Survey, vol. ii, 1894, p. 408. 

 I Proc. Ann. Phil. Soc, vol. xxxvi, 1898, p. 330. 



