PAPERS ON GEOGRAPHY AND GEOLOGY 199 



SOME QUESTIONS IX GENERAL AND PETROLEUM 



GEOLOGY WHICH ARE SUGGESTED BY OIL 



OCCURRENCES IN CRAWFORD COUNTY, 



PENNSYLVANIAN BEDS 



James H. Hance, State Geological Survey Division, 



Urbana 



SUMMARY 



Over a considerable part of Crawford County, oil pro- 

 duction from Pennsylvanian sands is conditioned by 

 other factors, perhaps as important as the LaSalle Anti- 

 cline. Certain features indicate a nearby source for the 

 oil and this may be important in future exploration work. 



GENERAL 



One of the controlling features, perhaps the most im- 

 portant, of the oil fields in southeastern Illinois is the 

 LaSalle Anticline which extends from the vicinity of La- 

 Salle southeast nearly to the Wabash River at St. Fran- 

 cisville. Productive territory has been developed 

 through Clarke, Crawford, Lawrence, and Wabash Coun- 

 ties for a distance of seventy miles, and although this 

 area of production varies in width up to sixteen miles, 

 commercial accumulation of oil extends to a distance of 

 eleven miles northeast from the axis on the less steeply 

 dipping flank. 



Thus far production has been developed from Pennsyl- 

 vanian sands on down to the Trenton limestone, but the 

 development in any one place is limited to a small por- 

 tion of the vertical range. (Martinsville area excepted.) 

 Thus in Lawrence County most of the oil produced comes 

 from rocks of Mississippian age. In Crawford County 

 production is chiefly from Pennsylvanian and Mississip- 

 pian rocks, and in Clarke County, the Pennsylvanian, 

 Mississippian and Ordovician rocks are each important 

 locally. 



All of this production is along the LaSalle anticline 

 and is clearly related to it. During the past eight years 

 detailed studies have brought to light certain features, 

 which when better understood may assist greatly in 



