GEOLOGICAL PAPERS. 95 



Coulterville syncline, the coal rises toward Pinckneyville and 

 forms an anticline between there and Duquoin. This is about 8 

 miles wide. The coal presnts a remarkable dip of over -100 feet 

 in about 2 J/2 miles, immediately east of Duquoin. This offers ex- 

 cellent opportunity for the migration of oil into the anticline and 

 as several wells already drilled indicate, the sands on the slope 

 are thoroughly saturated with water. The Duquoin anticline 

 extends to the southwest towards ]\Iurphysboro and is shown 

 by the coal contours recently published by E. W. Shaw on the 

 Murphysboro quadrangle. From Duquoin northward it probably 

 passes west of Tamaroa and Dubois, and between Nashville and 

 Ashley. It is considered to be a continuation of the Sandoval 

 "terrace," already spoken of. The crest of this structure is 

 higher at Duquoin than at Sandoval and hence has a slope down- 

 ward to the north of Duquoin. At Duquoin the dip is from about 

 400 feet above to several feet below sea level, while at Centralia 

 the dip is from sea level downward. The fold is narrowing in 

 its axial width northward from Duquoin. 



The most promising structural features along this section are 

 enumerated as follows : 



1. The Marissa flat. 



2. The Tilden anticline. 



3. The Duquoin anticline. 



4. The second Duquoin arch. 



The D-D cross-section (plate IV) was drawn from Marion in 

 Williamson County to Salem in ^Marion County. It crosses the 

 southern slope of the Illinois basin and shows the position of the 

 coal from south to north. The dip along the southern slope 

 of the basin is about 50 feet per mile. There is a slight flattening 

 of the coal between wells 5 and 6. A "terrace" occurs between 

 wells 8 and 9, south of Benton, and a slight bench is shown 

 at well No. 11. 



The E-E cross-section (plate V) is the most northern one and 

 is plotted along a line from Beardstown in Cass County to the 

 State line near Danville in Vermilion County. The section reveals 

 the relations of the lower rocks on the western side of the State ; 

 the shallow character of the Illinois basin in the northern part 

 of the State ; and the La Salle anticline. It is particularly valu- 

 able from a stratigraphical point of view, since the Chester rocks 

 are shown to be absent around Springfield and present to a small 

 degree in the basin at Decatur. The Pottsville is very thin along 

 this section. The only significant feature in the structure exists 



