SHAW I NEW AREA OF CARBONIFEROUS 555 



Devonian, and Mississippian formations, the oldest deposits of 

 the embayment extending farthe'st north and lying upon the 

 youngest Paleozoic beds. Among themselves, the embayment 

 formations, according to published descriptions, off-lap the young- 

 est outcropping farthest seaward and along the axis of the em- 

 bayment, and the oldest around the margins, or landward edge 

 of the area. 



The maps and descriptions indicate that central and southern 

 Massac County, Illinois, the second county up the Ohio River 

 from Cairo, is underlain by southward and southwestward dip- 

 ping Cretaceous and Tertiary beds that rest upon the eroded 

 edges of formations belonging for the most part far below the 

 top of the Mississippian series, and that the northern part is 

 occupied by outcrops of "Lower" and "Upper Mississippian" 

 formations and Quaternary deposits. The maps show that a 

 few miles to the east of the county is an area of Mississippian 

 rocks bordering Ohio River. 



It was therefore somewhat of a surprise to find a few years ago, 

 while the writer was doing some work in the section of Coastal 

 Plain Investigations, U. S. Geological Survey, outcrops of coal- 

 bearing rocks in eastern Massac County, and to find also some 

 of the immediately underlying Mississippian strata. The out- 

 crops, which occupy several square miles in the vicinity of Oliff, 

 were unexpected, both because the region is shown on maps as 

 being underlain with Mesozoic and Cenozoic formations, and 

 because according to available information the southern limit 

 of the Pennsylvanian, or coal-bearing rocks, is many miles to 

 the north, their horizon in Massac County being, to judge from 

 the maps, far above the present surface. However, it should 

 be remarked that not many miles to the east in Kentucky are 

 some small outliers of coal-bearing rocks. 



This small coal basin and the outcropping rocks of the Chester 

 group in the surrounding area are of especial interest, for they 

 furnish new information on the areal, economic, and structural 

 geology and on the physiography of the region. 



They show that Pennsylvanian and uppermost Mississippian 

 beds occur a good many miles south of the previously known 



