500 



GEOLOGY. 



Subdivisions. 



The following subdivisions of the Mississippian system are recog- 

 nized in the regions indicated: 



Mississippi River States. 1 



Ohio.z 



Pennsylvania. 3 



Maryland. 4 



4. Kaskaskia or Chester 



3. St. Louis 



2. Osage or Augusta (includ- 

 ing the Burlington, 

 Keokuk, and Warsaw) 



1. Kinderhook or Chouteau 



'7. Maxville 



6. Logan 



5. Black Hand 

 • 4. Cuyahoga 



3. Sunbury 



2. Berea grit 

 .1. Bedford' 



2. Mauch Chunk 

 1. Pocono 



3. Mauch Chunk 

 2. Greenbrier 5 



1. Pocono 



East of the Great Plains. 



In the early part of the Mississippian period, when the sea was 

 somewhat more expanded than is shown in Fig. 196 and less wide-spread 

 than is represented in Fig. 228, the eastern edge of the sea seems to 

 have been bordered by high land, for along the western border of 

 Appalachia coarse sediments (sands and gravels, now Pocono sand- 

 stone and conglomerate) were gathering. The land to the north and 

 south of the interior sea seems to have yielded finer sediments. In 

 the area east of the Cincinnati arch, the sediments which now con- 

 stitute the lower part of the Waverly series 6 were being deposited. 

 Much of this sediment may have come from the arch itself, which 

 may have been at first a peninsula and later an island. The area 

 of southern Michigan 7 was a sort of bay or enclosed sea into which 

 sediment was washed from the surrounding lands at the time the 

 lower part of the Waverly series was being deposited east of the Cin- 

 cinnati arch. The association of salt (brine) with the Michigan beds 



1 Williams, Bull. 80, U. S. Geol. Surv., p. 169. St. Genevieve was the term applied 

 by Williams to the upper part of the Mississippi system. 



2 Prosser, Jour, of Geol., Vol. IX, p. 215, and Vol. XI, p. 520. See also Am. 

 Geol., Vol, XXXIV, p. 335. 



3 Pennsylvania Repts. and folios of U. S. Geol. Surv. 



4 0'Hara, Maryland Geol. Surv., Allegany Co., pp. 109-13. 



^ The Greenbrier is absent in eastern Pennsylvania. It comes in as a lentil of 

 limestone farther west, and thickens southward, becoming an important formation 

 in Virginia, largely replacing the Mauch Chunk shale. See Brownsville-Connells- 

 ville folio, U. S. Geol. Surv. (Campbell.) 



6 Geol. Surv. of Ohio, Vol. VII, pp. 503-815. 



7 Geol. Surv. of Michigan, Vol. V and Vol. VII, Pt. II, Huron County. 



