380 ILLINOIS STATE ACADEMY OF SCIENCE 



has available extensive information of this kind. Bul- 

 letins are published frequently and cooperation is main- 

 tained with those interested in oil development. Based 

 on the study of the accumulated subsurface data and the 

 original surveys and surface observations of the Survey, 

 the accompanying map (Figs. 2 and 3) has been prepared 

 to show in a general way the location of the various oil 

 producing areas of Illinois, the localities where favorable 

 structures exist, and the proportion of those outlined 

 that have been tested and found productive. General in- 

 ferences may be drawn as to the probabilities of finding 

 further producing areas in Illinois and the general geo- 

 graphic position of the areas of greater promise. 



Outside of the actual producing areas in Illinois, with 

 which may be classed probable extensions, the remainder 

 of the State can be divided approximately into provinces 

 representing, according to our present knowledge, four 

 different grades of merit as to the chance of finding com- 

 mercial accumulations of oil: (1) best possibilities; (2) 

 possible; (3) improbable; and (4) very improbable. The 

 differentiation has been made largely on the basis of 

 known or expected presence of favorable structure. 



(1) An area of best possibilities may be described 

 as extending north from the common line of Cumber- 

 land and Clark counties where the LaSalle anticlinal up- 

 lift is developed into two folds, one axis continuing west 

 of north through LaSalle County, while the other appears 

 to run more directly north to Iroquois and Kankakee 

 counties. The area north of the producing fields immed- 

 iately along these axes has good possibilities where slight 

 cross folding is present. In this same class should be in- 

 cluded an area immediately west of the central struc- 

 tural basin, running south from western McLean County, 

 including the west portion of DeWitt and Macon counties, 

 the east half of Logan and Sangamon counties, of Chris- 

 tian, Montgomery, Macoupin, Madison, Bond, a west 

 portion of Fayette and Marion, Clinton, most of Wash- 

 ington, St. Clair, Randolph, Perry, Jackson counties, and 

 possibly in the southern part of the State, parts of Frank- 

 lin, "Williamson, Saline, Gallatin, and portions of ad- 

 joining counties to the south; and in addition, the area 



