508 



GEOLOGY. 



States, are given, along with the associated sections of the Pennsyl- 

 vanian (Carboniferous proper), on pp. 557-563. 



Reasons for Regarding the Mississippian a Distinct 



System. 



The withdrawal of the sea from a large part of the eastern interior 

 at the close of the Mississippian division of the Carboniferous period 

 exposed the newly deposited sediments to erosion. The exposure 

 was long and the erosion considerable. At the opening of the Coal 

 Measures period, as will be seen in the sequel, a large part of this area 



Fig. 230. — Composite diagrammatic section, showing the unconformity between 

 the Mississippian and Pennsylvanian systems in Iowa. (Keyes, la. Geol. Surv.) 



was again the site of deposition, and the new system rests uncon- 

 formably on the Mississippian over wide areas. 1 This is true in places, 

 and perhaps generally, in Missouri 2 (Fig. 232), Iowa 3 (Fig. 230) ; 

 Kansas, 4 probably in Illinois, in Indiana 5 (Fig. 231), Kentucky 6 and 



pian is often clearly separated from the Pennsylvanian, though not as a separate 

 system. 



1 Missouri Geol. Surv., Vol. VII, p. 422, and Vol. VIII, pp. 340 and 348; Iowa 

 Geol. Surv., Vol. IV, p. 282, and Vol. I, pp. 74 and 89; the Univ. Geol. Surv. of Kans., 

 Vol. I, pp. 17 and 147; Indiana Dept. of Geol., 20th Ann. Rept., p. 196 et seq., and 

 23d Ann. Rept., p. 101; Charleston, W. Va., Standing Stone, Chattanooga, Loudon, 

 and Wartburg, Tenn. ; Richmond and Loudon, Ky., and Gadsden, Ga., folios, US.. 

 Geol. Surv. 



2 Missouri Geol. Surv., Vol. VII, p. 424, and XII, Pt. II, pp. 31 and 209, and 22d 

 Ann. Rept., U. S. Geol. Surv., Pt. II, p. 88. 



3 Geol. Surv. of la., Vol. V, p. 321, Vol. VII, pp. 79, 210, 426, 503; Vol. IX, p # 

 265, and Vol. XII, pp. 82, 296, and 448. 



4 Univ. Geol. Surv. of Kans., Vol. I, pp. 16 and 147. 



6 22d Ann. Rept., Dept. of Geol. and Nat. Res., p. 17; and 23d Rept., p. 74, and 

 Fuller, Ditney folio, U. S. Geol. Surv. 



"Loudon and Richmond folios, U. S. Geol. Surv. 



