554 shaw: NEW AREA of carboniferous 



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A later map of Illinois 5 represents the Gulf embayment de- 

 posits in Illinois, except the Quaternary alluvium, by one color, the 

 heading in the legend being "Cretaceous-Tertiary." The north- 

 ern boundary is more irregular than on earlier maps and some 

 Paleozoic rocks ("Lower Mississippian") are shown on the 

 south side of the abandoned portion of the Ohio Valley. 



It may be remarked incidentally that only two of the maps 

 referred to show the deposits in this old valley and they do not 

 show them as connected through to the east or east-southeast 

 with the recent alluvium of the present course of the Ohio, 

 though in fact the deposits and the abandoned valley run from 

 the present channel of the Ohio. westward without interruption 

 to the present channel of the Mississippi. 



With the exception of Glenn's map, which does not differ- 

 entiate the Paleozoic, the various maps show the southern limit 

 of Pennsylvanian strata as trending in general east and west 

 through the northern part of the second row of counties north 

 of the Ohio (Union, Johnson, Pope, and Hardin). The latest 

 and most detailed map of this region shows a belt of "Upper 

 Mississippian" rocks occupying the middle and southern portions 

 of these counties, with some " Lower Mississippian" on the south, 

 some small areas of Devonian in the eastern part* (west-central 

 Hardin County), and some Devonian, Silurian, and Ordovician 

 on the west and southwest extending to the present channel of 

 the Mississippi opposite Commerce, Missouri. 



Earlier descriptions, particularly those of Worthen and Engel- 

 mann, 6 accord with the geologic maps later published. All indi- 

 cate southward-dipping Mesozoic and Cenozoic rocks in the 

 southern row of counties and northward-dipping Paleozoic rocks 

 in the country to the north, the southern limit of the Pennsyl- 

 vanian, or coal-bearing formations, being some distance north of 

 the Gulf embayment. The deposits in the embayment thus lap 

 over a part of the outcropping edges of the Ordovician, Silurian, 



Illinois State Geol. Survey, Provisional geologic map of Illinois. Scale 

 1 : 500,000. 1912. 



6 Worthen, A. H. Geology. Geol. Survey of Illinois, vol. 1. 1866. Contains 

 geology of Pulaski and Massac counties by Henry Engelmann, pp. 410-455. 



