574 



GEOLOGY. 



and water in the eastern part of North America during the Penn- 

 sylvanian period, was great, though perhaps not greater than during 

 other periods. 





*-* m& 





7 



s-' 





?B1 







/ \ 



;__-- ; 



■6'jof "* 



TO/' 



'.' ■ -' - 



+■*«''' 





.;■...•!! 







8 



•■ 





«'-*• 



n 





'-i_ ~ 







_' 



•»'-«' 







4^' 



ItO g4fl 



■55i: 



Fig. 257. — Sections of Illinois and Indiana Coal Measures; 1, shaft at Oglesby, La 

 Salle Co., 111.; 2, air shaft at Decatur, Macon Co., 111.; 3, shaft at Kinmundy,. 

 Marion Co., 111.; 4, boring at Galum Creek, Perry Co., 111.; 5, boring at Danville, 

 Vermilion Co., 111.; 6, connected section from South Vermilion and Parke Cos. 

 Ind. ; 7, connected section from Dugger and Linton, Sullivan and Parke Cos., 

 Ind.; 8, connected section from Henderson, Ky., and Evansville, Ind. (Ashley, 

 U. S. Geol. Surv.) 



Extent and relations of coal-beds. — The widespread distribution 

 of coal does not mean that any one marsh necessarily covered the 



Fig. 258. — Local unconformity in Coal Measures of central Iowa. (Keyes, la. Geol. 



Surv.) 



whole of any one great coal-field. Some of the coal-beds, however, 

 are known to be of great extent. Thus a single bed, the Pittsburg, 



Fig. 259. — Local unconformity in the Coal Measures; sandstone occupying " cut 

 out " in coal beds. Smoky Hollow mine, Marion Co., la. (Keyes, la. Geol. Surv.) 



is known to be workable over an area of some 6000 square miles 1 in 



1 White, West Virginia, Geol. Surv., Vol. II, p. 166. 



