86 ILLINOIS ACADEMY OF SCIENCE. 



plunging anticline, the convergence of the sands at the northern 

 end and the mergence of the dome into the fiat at the southern 

 end of the field. The sands are generally parallel with local 

 irregularities that seem due in most cases to the thinning and 

 thickening of the sand. The remaining sections are plotted cross- 

 wise to the fold and reveal the amplitude of the arch. 



The largest amounts of oil in the Lawrence county field are 

 in the extensive flat area in the southern half of the field, and 

 at a level of about sixty feet below the crest of the dome in the 

 northern division. 



The sands of Lawrence county show abundant water along the 

 lower flanks of the anticline and but little through the center of 

 the field, except in the lower Bridgeport and Buchanan sands. 

 These Pottsville rocks appear well saturated with water over the 

 entire field and into the limbs of the La Salle fold. The under- 

 lying Chester sands are not uniformly saturated with water, but 

 seem to have lines of saturation along the limbs of the fold, more 

 particularly along the western side. 



SUMMARY. 



The features of the structure maps and their individual oil, 

 gas and salt water relations, just described, are sufficiently simi- 

 lar to permit general conclusions regarding the accumulations of 

 oil and gas in Crawford and Lawrence counties. These conclu- 

 sions add to the general fund of evidence relating to the accumu- 

 lation of oil and gas in raised rocks. 



The greater part of Illinois lies within the Eastern Interior 

 coal basin, which is, broadly speaking, an extensive spoon-shaped 

 basin, with its axis extending along a line, through Cerro Gordo, 

 Lovington and Olney and into its deepest part in Wayne, Hamil- 

 ton and Edwards counties. The east side of the basin rises into a 

 strong longitudinal fold known as the La Salle anticline. The 

 ascent is at the average rate of about fifty feet per mile, but it 

 is more rapid in Lawrence county, as shown by contours of the 

 very sharp apex of the anticlinal dome. The basin and lower 

 flanks of the fold are known to yield abundant water in all the 

 sands which are productive in the main fields. The uppermost 

 part of the flanks of the major fold contain abundant oil. The 

 western limits of the fields are abrupt, and beyond this line the 

 sands are wholly water-bearing. Enough data are at hand to 

 conclude that this is a line of water saturation and that above 

 this line and over the fold most of the sands are oil-bearing. 



