GEOLOGICAL PAPERS. 89 



such as anticlinal folds, dips of coals, oil seeps, depths to the oil 

 sands, etc. The determination of structural leatures outside of 

 the main fields seemed formidable because of the immense ex- 

 panse of flat territory, so covered with drift as to conceal the 

 sequence of formations and practically all evidence of folding 

 and faulting. The only means available was to construct several 

 geological cross-sections of Illinois and to point out the irregu- 

 larities occurring in some key horizon. The folds ser\-e to out- 

 line prospective drilHng areas to the oil operators but the adjoin- 

 ing basins or slopes are not so favorable. 



Plate 1 indicates the location of the sections which were con- 

 structed. 



The general sections were chosen along lines showing the 

 greatest number of wells and coal bores and at the same time 

 crossing the great structural basin of IlHnois. The identification 

 or correlation of various beds in each section presents a general 

 idea of the stratigraphy and structure of the lower portion of the 

 State. The four sections presented here include only a portion 

 of the v.ork accomplished by the Survey. The cross-sections 

 were constructed by plotting records with uniform symbols and 

 scale. They are located with respect to their distance from the 

 nearest town and to their position above sea level. Correlation 

 lines, drawn between similar formations in adjoining records, 

 picture any rise or fall. Thus section A-A. (plate II.) giving 

 the most complete geological data across the State, presents a 

 complete picture of the great structural basin of central IlHnois. 

 The section is drawn from St. Louis. Mo., to Vincennes. Ind., 

 and crosses the Sandoval and Lawrence County oil fields. In 

 this and the other sections, there is indicated a conspicuous 

 spoon-shaped basin, with its long axis paralleling the LaSalle 

 anticline and extending from the north line of Stephenson Coun- 

 ty past LaSalle, Cerro Gordo, Lovington. Olney, and continuing 

 to the southwest county of Indiana. The deepest part of the 

 basin lies in the vicinity of Wayne, Hamilton. Edwards, and 

 White counties, where the rocks lie comparati^ ely flat and the 

 basin broad. Towards this basin, with local exceptions, all the 

 rocks of Illinois and of Western Indiana, dip gently. Attention 

 is called to the key horizon or the No. 6 coal, which is definitely 

 known over about one-half the section, while in the remainder, it 

 is doubtfully identified. 



The accompanying printed sections indicating the order and 



