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STATE OF ILLINOIS 
 DEPARTMENT OF REGISTRATION AND EDUCATION 
 
 A. M. SHELTON, Director 
 
 DIVISION OF THE 
 
 STATE GEOLOGICAL SURVEY 
 
 M. M. LEIGHTON. Chief 
 REPORT OF INVESTIGATIONS-NO. 4 
 
 CARBON RATIOS AND PETROLEUM 
 IN ILLINOIS 
 
 BY 
 GAIL F. MOULTON 
 
 PRINTED BY AUTHORITY OF THE STATE OF ILLINOIS 
 
 URBANA, ILLINOIS 
 1925 
 
STATE OF ILLINOIS 
 DEPARTMENT OF REGISTRATION AND EDUCATION 
 
 DIVISION OF THE 
 
 STATE GEOLOGICAL SURVEY 
 
 M. M. LEIGHTON, Chief 
 
 Committee of the Board of Natural Resources 
 and Conservation 
 
 A. M. Shelton, Chairman 
 
 Director of Registration and Education 
 
 Kexdric C. Babcock 
 
 Representing the President of the Uni- 
 versity of Illinois 
 
 Edson S. Bastin 
 Geologist 
 
 Schnepp & Barnes, Printers 
 
 Springfield, III. 
 
 1925 
 
 43276—1000 
 
GAR HON RATIOS AND PETROLEUM 
 IN ILLINOIS 
 
 By Gail F. Moulton 
 
 OUTLINE 
 
 [•AG E 
 
 Introduction 5 
 
 Use of data 5 
 
 Sources of information 5 
 
 Accuracy of carbon ratios 6 
 
 Structural features of Illinois 10 
 
 Relation of oil fields to structural features 11 
 
 Fields along the La Salle anticline 11 
 
 Minor western fields 11 
 
 Relation of coal character to structural features 11 
 
 Carbon ratios 11 
 
 Moisture content 14 
 
 Isohume determinations from carbonaceous shales 14 
 
 Conclusions concerning oil possibilities 15 
 
 Choice of limiting ratios 15 
 
 Areas appearing to have special merits 17 
 
 Value of carbon ratios 18 
 
 ILLUSTRATIONS 
 
 FIGURE 
 
 1. Generalized structure map of Illinois 8 
 
 2. Illinois oil and gas fields 9 
 
 3. Isocarb map of Illinois for No. 6 coal 12 
 
 4. Isohume map of Illinois coal 13 
 
 5. Horizons with oil possibilities according to carbon ratios 16 
 
 TABLES 
 
 1. Variations of carbon ratios between the various coals in Illinois 7 
 
 2. Relation of carbon ratios to sand and oil character 15 
 
 3. Limiting carbon ratios for oil producing horizons in certain localities.. 17 
 
INTRODUCTION 
 
 In the decade since White 1 first called attention to the interrelation of 
 the effects of metamorphism on coal and petroleum, the relation has been 
 further investigated in several of the important oil producing states. Thus 
 far, carbon ratios (the ratio of Fixed Carbon to the sum of Fixed Carbon 
 plus Volatile Matter) have been very useful in pointing out areas in which 
 the processes of metamorphism have been so pronounced that the chances 
 of rinding commercial accumulations of petroleum are slight. The possi- 
 iblity of their use in locating areas of greater deformation favorable to oil 
 occurrence in regions of slight folding, has not been stressed, but also de- 
 serves consideration. 
 
 Petroleum investigations in Illinois are greatly hampered by the occur- 
 rence of the thick cover of glacial drift and the shallow dissection of the 
 surface. Detailed determinations of structural conditions have depended 
 largely upon the interpretation of well logs. For considerable areas in the 
 State, such information is scanty and not very reliable. Consequently, it 
 seems desirable to investigate carbon ratios in Illinois coals to assist in de- 
 lineating areas in which general deformation has occurred. In such areas 
 the chances of finding structures suitable for the accumulation of petroleum 
 would be greater than in relatively undisturbed areas, and special attention 
 would be deserved. 
 
 In addition to the question of choice of areas for further investigation, 
 carbon ratios have possibilities in helping to solve several related problems 
 such as : ( 1 ) consideration of possibilities of oil production in the faulted 
 area in southern Illinois; (2) the deepest horizon which should be tested 
 in favorable structures in various regions of the State; (3) relation between 
 carbon ratios and moisture content of coals; (I) the effects of depth of 
 burial and unconformities on carbon ratios, and (5) the reason for the 
 dominance of gas production in western Illinois as contrasted with that of 
 oil in eastern Illinois. 
 
 USE OF DATA 
 
 Sources of Information 
 
 For a number of years Illinois has held an important place as a coal 
 producer. Consequently, a large amount of information is available con- 
 cerning the character of the coal. Most of the analyses have been compiled 
 
 •Whit., David, Some relations in origin between coal and petroleum: Wash. Acad. 
 Bci. Jour. Vol. 6, pp. 189-212, 1915. 
 
6 CARBON RATIOS AND PETROLEUM IN ILLINOIS 
 
 and published. 2 Carbon ratios were computed from the original analyses 
 for about 350 mines, and in mosl cases the re nil used was an average of 
 
 three or more analyses. All of the analyses used were made either by the 
 U. S. Bureau of Mines or the Fuel Laboratory of the University of Illi- 
 nois. The close agreemenl of results obtained by these two laboratories is 
 probably not excelled by any other two in the country. For that reason the 
 data used are of uniformly high quality. 
 
 \('( URACY OP' CaI BON 1\ VTIOS 
 
 The uncertainty i ; carbon ratio value corresponding to permissible 
 
 variations in the results of analysis was calculated in order to de ermine the 
 minimum change in carbon ratio which should he considered significant. 
 The method of computing this minimum is as follows: 
 
 Let A he the volatile matter, B the fixed carbon, and D the ash plus 
 moisture. Then A + B-f ') - 100 per cent and B / (A + B ) = the 
 carbon ratio. In order to determine the variation due to permissible errors 
 in analysis, the use of simple differen ial ca'culus is advisable. The equa- 
 tions which follow show the steps taken in deriving the formula. 
 
 B 100— (A +D) 
 
 = (Two expressions for the carbon ratio) 
 
 A + B 100 — /) 
 
 Differentiating: 
 
 B \ (100 — D) ( — dA — <W) + (100 — .1 — D) (ID 
 
 „(-£-) 
 
 V (A + B) / 
 
 < (-M 
 
 \U + B) J 
 
 (100 — D)- 
 or 
 
 B \ (100 — ID dA -- lOOdD + DdD + 100 dl) — AdD — DdD 
 
 (100 — D)' 
 
 (100 — D) (1A + Ad I) iIA AdD 
 
 Combining like terms gives = + 
 
 (100—")- 100— D (100 — uy 
 
 <1A AdD 
 
 or the uncertainty of carbon ratio = + in which dA is 
 
 100 — D (100 — DY- 
 
 the permissible error in volatile matter and dD is the permissible error in non- 
 combustible matter. 
 
 For Illinois coals the standard limits of error give the values dA= 
 1.00 per cent, and dD=0.8 per cent. By using these values and taking the 
 value for I) and A from the analyses of various Illinois coals, the uncertainty 
 in carbon ratio was found to vary from 1.18 to 1.38 according to the local 
 condition of the coal. 
 
 If each datum point on the map (fig. 3) had only one analysis as its 
 source of information, variations in carbon ratios of 1.25 per cent would 
 he of doubtful significance. The values used, however, were the result of) 
 
 ! Hawley, G. W., Analyses of Illinois coals: 111. Jlin. Investigations Bull. 27A, 1928 
 (Includes analyses previously published by tin- r. S. Bureau of Mines.) 
 
CARBON RATIOS AND PETROLEUM IX ILLINOIS . 
 
 averaging several analyses. This process reduced the probable error to at 
 least one-half the computed limit. Accordingly, variations of one per cent 
 in carbon ratio are considered significant, and fairly uniform changes of 
 smaller value are worth notice. In order to show all authentic details of 
 carbon ratio variation, isocarbs were drawn at intervals of two per cent. 
 
 The law of Hilt, that there is a progressive increase of fixed carbon in 
 successively older coal beds in passing downward in a stratigraphic section, 
 was considered in Illinois. David White 3 cites several exceptions. If the 
 law is exact, the increase in carbon ratio from one coal to the next in a con- 
 formable series would depend on the stratigraphic interval. If an uncon- 
 formity occurs between two coals, the lower should show an abrupt increase 
 in carbon ratio. 
 
 In Illinois several coal beds are important enough to be mined. In a 
 few localities samples from two or more coals have been analysed. These 
 analyses have been compared to check the law of Hilt and to determine the 
 carbon ratio correction for coals other than No. (i. Although in certain 
 cases modifications of results were probably introduced by errors in coal 
 correlation, a preliminary suggestion of the effects on carbon ratios was ob- 
 tained. These are shown in Table 1. Illinois coals have been given con- 
 secutive numbers beginning with No. 1 at the bottom. 
 
 Table 1. Variations of carbon ratios between the various coals in Illinois 
 
 County 
 
 Cot 
 
 1 
 
 Carbon 
 ratio 
 
 Comments on variations 
 
 Fulton 
 
 No. 
 
 5 
 
 51.7 
 
 No significant difference 
 
 
 No. 
 
 1 
 
 51.8 
 
 
 McLean 
 
 No. 
 
 5 
 
 48.8 
 
 No significant difference 
 
 
 No. 
 
 2 
 
 49.6 
 
 
 Gallatin 
 
 No. 
 
 6 
 
 57.4 
 
 Increase of 1.3 marks unconformity 
 
 
 No. 
 
 5 
 
 58.7 
 
 
 Vermilion 
 
 No. 
 
 7 
 
 50.8 
 
 Increase of 2.3 marks unconformity 
 
 
 No. 
 
 6 
 
 53.1 
 
 
 Jackson 
 
 No. 
 
 6 
 
 57.4 
 
 Increase of 2.8 marks unconformity 
 
 
 No. 
 
 2 
 
 60.2 
 
 
 As a result of a consideration of the available data in Illinois, it appears 
 that the effect of the difference in depth is not significant if the series is con- 
 
 White, David, The origin of coal: U. S, Bur. Mines Hull. :;s;. pp. 125-1! 
 
 1913. 
 
CARBON RATIOS AND PETROLEUM FN [LLINOIS 
 
 JO DAVIESS STEPHENSON I WINNEBAGO, g , „.,„, , , LAK£ 
 
 ILLINOIS J ogle 
 
 - Joe^lb| ; ' E | 0UD4&t | 
 
 -I-trM V 
 
 ' ILL 
 
 WILLIAMSON | SALINE 
 
 L-Zone of 
 . HXfoScN faulting 
 JOMNSONpyfEI-'^J 
 
 Fig. 1. Centralized structure map of Illinois. Contours on 
 approximate horizon of No. 2 coal. 
 
CARBON RATIOS AND PETROLEUM IN ILLINOIS 
 
 Fig. 2. Illinois oil and gas fields. 
 
10 CARBON RATIOS AND PETROLEUM IN ILLINOIS 
 
 formable. This apparent exception to the law of Milt may arise from the 
 small thickness of beds between the coals sampled (about 250 feet, maxi- 
 mum) or may be clue to a lack of critical data. In case the coals arc sepa- 
 rated by an unconformity, however, there is a marked increase in carbon 
 ratio of the lower coal. These differences seem to be pronounced enough 
 to be of value in coal correlation. 
 
 No. (i coal was chosen as the standard, for it is one of the most exten- 
 sive beds in the Siate. Because the No. <i coal is separated from both the 
 underlying and overlying coals by an unconformity, a correction is necessary 
 in the carbon ratios of the other coals in order that the results may be com- 
 parable. The following corrections were applied to reduce results to No. 6 
 coal : 
 
 Gallatin County — Subtract 1.3 from carbon ratios of No. 5 coal. 
 
 Vermilion County — Add 2.3 to carbon ratios of No. 7 coal. 
 
 Jackson County — Subtract 2.8 from No. 2 coal carbon ratio. 
 These ratio corrections were also applied to coals in the vicinity of the places 
 For which they were determined. 
 
 STRUCTURAL FEATURES OF ILLINOIS 
 
 In order to appreciate fully the significance of the carbon ratios in Illi- 
 nois, it is first desirable to have a general idea of the main known structural 
 features of the State ( fig. 1 ), so that the relation between these features and 
 the configuration of the isocarbs will he apparent. 
 
 The La Salle anticline is one of the most prominent structural features 
 of Illinois. It may be traced from the north central part of the State in a 
 direction a little east of south for most of the length of the State to a point 
 where it crosses Wabash River into Indiana. The structural contours (fig. 
 1 ), show that the dip on the west limb of the fold is much steeper than that 
 on the east. The folding along this axis began in pre-Pennsylvanian time, 
 •but was continued at the end of the Pennsylvania!! deposition, so that the 
 structure in the lower rocks is similar to that of the coals, hut is more pro- 
 nounced. 
 
 The Duquoin anticline is another prominent fold. It extends through 
 the south central portion of the State in a north-south direction. In this 
 case, the steeper dip is on the east side of the fold. As figure 1 shows, the 
 west side is rather indefinite, and is not marked by west dips. 
 
 The interior basin lies between the steeply dipping east limb of the 
 Duquoin anticline on the west, and the steeply dipping west limb of the 
 La Salle anticline on the east, and, as the map shows, includes a large part 
 of the State. In most portions of the basin the coals are at a considerable 
 depth. This is due to both the structural depression and greater thickness 
 of the Pennsylvanian sediments. The greater thickness of the sediments and 
 the greater abundance of liner clastic materials point to the existence of this 
 basin during the early Pennsylvanian at least. 
 
CARBON RATIOS AND PETROLEUM IN ILLINOIS 1 1 
 
 The southern zone of faulting was the scene of more vigorous dynamic 
 adjustments. Complex faulting and minor igneous activity characterize this 
 region. As a result of greater relative uplift, the Pennsylvanian has been 
 largely removed from this area. Only along the north edge of the zone of 
 faulting is it possible to determine carbon ratios. Although much of the 
 faulting may be post-Chester and pre-Pennsylvanian, a large part of it oc- 
 curred after the close of the Pennsylvanian. Only a few of the major faults 
 are indicated in figure 1. 
 
 RELATION OF OIL FIELDS TO STRUCTURAL FEATURES 
 Fields Along the La Salle Anticline 
 As might be expected in an area of moderate disturbance, the principal 
 oil fields are located along one of the principal lines of folding. More than 
 ninety per cent of the present oil production of the State comes from these 
 fields on the La Salle anticline. For various reasons, the producing area 
 has been nearly continuous along much of the fold. This relation is strik- 
 ingly brought out by a comparison of figures 1 and '!, which show the loca- 
 tion of the La Salle anticline and the producing area respectively. The pro- 
 ducing horizons include the Trenton, the Kinderhook and the Mississippian 
 lime of the lower Mississippian, the Chester, and the Pennsylvanian. 
 
 Minor Western Fields 
 Three of the minor pools in Illinois are located on and near a broad 
 northern extension of the Duquoin anticline. The other pools in the west- 
 ern part of the State are located on folds which have no established con- 
 nection with the major structural features of the State. 
 
 RELATION OF COAL CHARACTER TO STRUCTURAL 
 
 FEATURES 
 
 Carbon Ratios 
 
 A comparison of the structural contours in figure 1 and the isocarbs 
 in figure 3 shows that the zones disturbed by folding are closely followed 
 by increases in the carbon ratios in the coal. The folding of the La Salle 
 anticline and the Duquoin anticline in particular have caused zones of high 
 carbon ratios which project for many miles into areas of lower carbon ratios. 
 
 The isocarb map also shows clearly that the disturbances accompanied 
 by faulting in the southern part of the State caused a greater regional meta- 
 morphism than is general in the central and north parts of the State. 
 
 One of the most interesting features brought out by the isocarb ma]) is 
 the tongue of high carbon ratios which extends northwest from central 
 Tazewell County to Rock Island County. The existence of this area of 
 higher ratios had not been suspected because there is no structural feature 
 of major importance known there. It would appear that the carbon ratios 
 
12 
 
 CARBON RATIOS AND PETROLEUM IN ILLINOIS 
 
 FlG. 3. Isocarb map of Illinois for No. 6 coal 
 
CARBON RATIOS AND PETROLEUM IN ILLINOIS 
 
 13 
 
 Fig. 4. Isohume map of Illinois coal. 
 
II CARBON RATIOS AND PETROLEUM IX ILLINOIS 
 
 in this instance will be useful in pointing ou1 a locality deserving inure thor- 
 ough investigation. 
 
 Moisture Content 
 
 An unpublished map drawn by (i. II. Cady suggested the possibility of 
 using the moisture content of coals as a means for interpreting the effective- 
 ness ol metamorphism. A new ma]) has been prepared, making use of more 
 recent available data. The mapping of the moisture content of Illinois coals 
 did not give as satisfactory results in all parts of the State as the carbon 
 ratios did, duv probably in part to the lack of consistent handling and treat- 
 ment of the samples before analysis. In Franklin and Williamson coun- 
 ties the results were more satisfactory. As a large number of analyses 
 would tend to help average out errors, such regions should show the besl 
 results. 
 
 In analysis, the permissible error in moisture determination is ().:i per 
 cent for coals of the type found in Illinois. An examination of the results 
 of moisture determinations suggests that ordinarily variations of L.5 per cent 
 may he considered significant. Accordingly, the lines connecting points of 
 equal moisture content were drawn at intervals of two per cent. 
 
 For convenience, it is proposed to call the lines connecting points of 
 equal moisture "isohumes". The isohumes shown in figure 4 are very 
 closely parallel to the isocarbs (fig. 3), It should be noted that the value 
 of the isohumes decreases as regions of greater metamorphism are ap- 
 proached, and that this is in direct contrast to the changes in carbon ratios. 
 Also, the value of the isohumes is subject to more considerable variations 
 as the critical carbon ratios are approached. This is well shown in south- 
 ern Illinois, where die isohumes are closer together than the isocarbs. 
 
 I SOUL' MI-". DETERMINATIONS FROM CARBONACEOUS 
 
 SHALES 
 
 Several points should he considered in connection with the possibility 
 of using the moisture content of coals and other carbonaceous rocks, as an 
 indicator of the effectiveness of metamorphism. First, the carbon ratios of 
 impure coals and carbonaceous shales are subject to great variation, due to 
 permissible errors in analysis. As an example, may he cited a coal with a 
 carbon ratio of 50 per cent, and with noncomhustihle material making up 
 90 per cent of the whole. From the formula previously derived, the pos- 
 sible variation in carbon ratio is found to he 13 per cent. This fact may be 
 the explanation of the failure of attempts to use carbon ratios from rich 
 organic shales. 
 
 The moisture determination would not he affected in a similar manner, 
 and should still he dependable within a limit of I.-") per cent. These consider- 
 ations suggest that standard methods for the sampling of fine shales and the 
 determination of moisture content should he established, in order to test 
 
CARBON RATIOS AND PETROLEUM IN ILLINOIS 
 
 15 
 
 this possible means of measuring the effectiveness of metamorphism in re- 
 gions which have no coal. In view of the fact that changes in metamor- 
 phism near the critical limit for petroleum accumulation have a marked 
 effect on the moisture content, this method of attacking the problem seems to 
 have great possibilities. 
 
 CONCLUSIONS CONCERNING OIL POSSIBILITIES 
 Choice of Limiting Ratios 
 
 The effect of metamorphism at depths below the coals is a variable 
 factor which may be a serious obstacle to the unrestricted use of carbon 
 ratios in outlining the possible oil areas in Illinois. The numerous uncon- 
 formities to be found in the stratigraphic section require some rough evalu- 
 ation so that conclusions can be reached regarding depths to which drilling 
 is advisable for any given carbon ratio. Probably the simplest and most 
 reliable method for making such determinations is to examine conditions in 
 the producing fields of the State, and, using these conditions as a standard, 
 to detect the presence of local variations which demand an adjustment in 
 the carbon ratio limit for possible oil production. From such information, 
 it is proposed to estimate the effects of depth and unconformities in terms of 
 oil possibilities. 
 
 According to available information, most of the Illinois oil production 
 comes from areas with carbon ratios lying- between 54 and 57 for the No. 6 
 coal. Table 2 shows the highest carbon ratios known near producing areas 
 for each of the oil sands. 
 
 Table 2. Relation of carbon ratios to sand and oil character 
 
 Age 
 
 County 
 
 Depth 
 
 Character 
 
 Carbon 
 ratio 
 
 Gravity 
 of oil 
 
 Chester 
 
 Jackson 
 
 850 
 
 Porous sand 
 
 56 
 
 (mainly 
 
 gas) 
 
 Degrees 
 Bait me 
 
 
 
 Chester 
 
 Wabash 
 
 1400 
 
 Porous sand 
 
 57 
 (probably) 
 
 35 
 
 Mississippian 
 
 Clark 
 
 700 
 
 Soft 
 
 55 
 
 32 
 
 lime 
 
 
 
 
 
 
 Mississippian 
 
 Lawrence 
 
 1700 
 
 Open lime- 
 stone 
 
 56 
 
 
 lime 
 
 
 Lowest Mississippian 
 
 Clark 
 
 1400 
 
 Fine sandy 
 
 55 
 
 38.7 
 
 (Kinderhook) 
 
 
 
 siltstone 
 
 
 
 Silurian 
 
 McDonough 
 
 430 
 
 Open sandy 
 lime 
 
 52 
 
 
 
 
 Trenton 
 
 Clark 
 
 2300 
 
 Hard, tight 
 
 55 
 
 37 
 
 Trenton 
 
 Monroe 
 
 500 
 
 Coarsely 
 crystal- 
 line 
 
 53 
 
 30.1 
 
in 
 
 CARBON RATIOS AND PETROLEUM IN ILLINOIS 
 
 Fig. 5. Horizons with oil possibilities according to carbon ratios. 
 
CARBON RATIOS AND PETROLEUM IX ILLINOIS 
 
 1 
 
 Certain relations are suggested by the tabulated information. First, it 
 seems probable that the Trenton of eastern Illinois has not been a good oil 
 producer, because the metamorphism active there made a substantial reduc- 
 tion in the natural porosity of the rock. In Monroe County, metamorphic 
 effects were not as great, so the Trenton is more open and productive. The 
 carbon ratios indicate this relation. Second, the difference in the character 
 of the production found in the Chester in Wabash and in Jackson counties 
 may be explained as due to a greater amount of pre-Pennsylvanian move- 
 ment in the latter place. Certainly in southwestern Illinois, there was pre- 
 Pennsylvanian folding, and recent work indicates that it was accompanied 
 by faulting. 4 Nothing very definite is known about the transition in south- 
 eastern Illinois, but the occurrence of heavier oil is suggestive of milder con- 
 ditions. If this variation leads to the conclusion that such a difference in 
 effectiveness of the pre-Pennsylvanian movements did exist, then it is neces- 
 sary to take a lower carbon ratio for the limit of possible Chester produc- 
 tion in the southwestern part of the State than in the southeastern. Ac- 
 cordingly, figure 5 showing zones with various possible producing horizons 
 does not have the boundaries of those zones strictly parallel to the isocarbs. 
 
 In determining the lowest horizon with possibilities of oil production, 
 the following carbon ratios were chosen as limits: 
 
 Table 3. Limiting carton ratios for oil producing horizons in certain localities 
 
 Horizon 
 
 Limiting value 
 
 Locality 
 
 Pennsylvanian 
 
 62 
 
 Southern Illinois 
 
 
 Chester 
 
 58 
 
 Southwestern Illinois 
 
 
 Chester 
 
 59 
 
 Southeastern Illinois 
 
 
 Lower Mississippian 
 
 56 
 
 Southwestern Illinois 
 
 
 Lower Mississippian 
 
 57 
 
 Southeastern Illinois 
 
 
 Silurian-Devonian 
 
 55 
 
 Southwestern Illinois 
 
 
 Smirian-Devonian 
 
 56 
 
 Other parts 
 
 
 Trenton 
 
 54 
 
 Southwestern Illinois 
 
 
 Trenton 
 
 55 
 
 Other parts 
 
 
 Areas Appearing to Have Special Merits 
 
 In searches for new oil pools in Illinois, it will probably be advisable 
 generally to limit consideration to areas having oil possibilities at least in the 
 Chester, and preferably in the lower rocks as well. Further, a concentration 
 
 4 Ekblaw, G. E.. Post-Chester, pre-Fennsylvanian faulting in the Alto Pass area : 
 State Acad. Sci., Springfield Meeting, 1025. 
 
L8 CARBON RATIOS AND L'ETKOLEUM IX ILLINOIS 
 
 nf attention on certain zones of locally higher carbon ratios is desirable and 
 justified. Such areas are the central pari of the La Salle anticline, the north- 
 ern part of the Duquoin anticline, and the area of high carbon ratio exte id 
 ing from Tazewell County to Rock Island County. 
 
 Value of Carbon Ratios 
 
 Carbon ratios of Illinois coals change in such a manner that the isocarbs 
 parallel the structural contours. On the basis of the carbon ratios, it is 
 possible lo eliminate deep testing in certain areas, and to eliminate other 
 areas entirely as probable oil producers, even if favorable structural features 
 should be found. An equally useful result is that some of the areas of 
 greatest promise are outlined. 
 
:CHER'S" 
 
 IBRARY BINDERS 
 507 3. Goodwin 
 UrbanB,IlL