78 



PENNSYLVANIAN SPORES OF ILLINOIS 



species which are represented by a few 

 specimens. These have not been described, 

 but the new genera are to be described by 

 another author from an area where more 

 abundant specimens have been found. Ten 

 species are restricted to the five coal beds of 

 this group and 21 species either originate 

 or terminate their geologic range in the 

 Carbondale group. 



McLEANSBORO GROUP 



The term McLeansboro was first applied 

 by DeWolf (1910) as a formational name 

 for rocks which overlie No. 6 coal bed in 

 Illinois. Jon A. Udden's description 

 (1906) of the cores of the borings at Dela- 

 field and Elm Grove in Hamilton County 

 was used as representative of the Mc- 

 Leansboro succession. Weller (1940) 

 raised the McLeansboro formation to the 

 rank of a group and introduced new forma- 

 tional units on a cyclothem basis. 



The McLeansboro formation according 

 to DeWolf included all Pennsylvanian 

 strata above No. 6 coal bed. Spore studies, 

 on the other hand, provide evidence in 

 agreement with that produced by Dunbar 

 and Henbest (1942) that there was a 

 major change in fauna and flora shortly 

 after the beginning of McLeansboro dep- 

 osition but prior to accumulation of the 

 Trivoli (No. 8) coal bed. Evidence indi- 

 cates that the Carbondale group should 

 extend beyond the position of the present 

 conventional upper boundary, at the top of 

 No. 6 coal bed, to the position of the 

 paleontologic change. The Carbondale- 

 McLeansboro boundary at such a position 

 would conform essentially to the Des 

 Moines-Missouri boundary of the Mid- 

 continent region. This matter is discussed 

 further in comments on the plant spores of 

 the No. 8 coal bed. 



The maximum thickness of McLeansboro 

 strata appears to be more than 1200 feet 

 in central and eastern Illinois (Weller, 

 1945). These strata are believed to be 

 equivalent to the upper third of the Des 

 Moines series, all of the Missouri, and 

 possibly a portion of the Virgil series of the 

 Midcontinent region, also to the upper 



Allegheny and all of the Conemaugh of 

 eastern United States and possibly to the 

 Westphalian D and lower Stephanian of 

 Europe. 



The McLeansboro group contains nu- 

 merous prominent marine limestones, many 

 thin and more or less lenticular coal beds, 

 a predominant amount of shale, siltstone, 

 and sandstone strata. In the shale beds 

 particularly there are numerous layers of 

 well preserved (not fragmentary) plant 

 compression fossils. Conglomerates and 

 variegated shale beds, although of local 

 occurrence and not prominent members of 

 the McLeansboro sediments, have fairly 

 definite stratigraphic positions and geo- 

 graphic distribution. 



Cooper (1946, p. 27) remarks: "As 

 indicated in the stratigraphic summary the 

 correlation of Illinois coal beds above the 

 Shoal Creek limestone with those of the 

 Midcontinent are uncertain and those in- 

 dicated on the chart (fig. 2) are tentative 

 and approximate, based on the analysis of 

 the ostracode faunas that have been studied 

 to date." Certainty of correlation and the 

 sequence of the coal beds based on spore 

 studies above the Shoal Creek are in doubt 

 because the coal beds are lenticular, making 

 it necessary to study numerous samples 

 in order to include all of the coal beds that 

 would be present in a composite section. 

 While many coal beds have been studied, 

 our information is still believed to be in- 

 complete. Therefore, the sequence of beds 

 for this portion of the McLeansboro sec- 

 tion is regarded as tentative and subject to 

 change in the light of additional informa- 

 tion. The coal beds which have been 

 studied contain many guide fossils indi- 

 cating rapid changes in the plant life. These 

 guide fossils are essential if it is going to be 

 possible to correlate the coal beds of this sec- 

 tion. Present indications suggest that the 

 fossil spores promise to play an important 

 role in the solution of the many correlation 

 problems of the upper McLeansboro section 

 in Illinois. 



Jamestown Coal Bed 



The Jamestown coal bed lies between the 

 Herrin and the Jamestown limestones. 



