CORRELATION OF ILLINOIS COAL BEDS 



The main objective of this investigation 

 was to explore the value of fossil spores, 

 found mainly in coal beds, as guide fossils 

 for correlation purposes. Because little pre- 

 vious work had been done in this field it 

 was important to know ( 1 ) whether or not 

 spores occur in sufficient abundance to be 

 useful, and (2) whether the evolution and 

 succession of Pennsylvanian plants was 

 rapid enough to produce important changes 

 in spore population between the time rep- 

 resented by successive beds or groups of 

 beds. In this connection it may be pointed 

 out that the spore distribution chart (in 

 pocket) records the presence of 130 species 

 assigned to 19 genera. Spores were abun- 

 dant in nearly all of the coal samples 

 macerated. The facts that genera and 

 species are numerous, and that 67 out of 

 130 species have restricted ranges, and 33 

 other species are restricted to Pennsylvanian 

 groups in Illinois or have important geologic 

 ranges, indicate relatively rapid plant 

 succession and evolutionary changes. These 

 spores therefore seem to fulfill the require- 

 ments of satisfactory guide fossils. 



These conclusions could not be reached 

 until the spore population of numerous coal 

 beds had been determined. It was neces- 

 sary, therefore, to sample numerous coal 

 beds and obtain fossil collections from 

 several samples from which lists were com- 

 piled. The usefulness of the spores as 

 guide fossils was indicated fairly early in 

 the studies, after which the compilation 

 of fossil lists representative of the various 

 coal beds seemed of greater importance than 

 the demonstration of their usefulness. At 

 the same time the additional evidence added 

 weight to the conclusion previously reached. 



In the following pages the fossil spores 

 characteristic of most of the coal beds in 

 the Pennsylvanian system of Illinois are 

 listed by coal bed. It is evident that a vast 

 amount of fossil material is available. It 

 was scarcely necessary to assemble special 

 evidence that evolutionary changes and 

 plant succession were of sufficient impor- 



tance to provide many species of spores of 

 restricted ranges. Actually the matter of 

 prime interest came to be the identification 

 of the spores characteristic of the different 

 coal beds or unit groups of Pennsylvanian 

 beds. 



In carrying on the census of spore popula- 

 tion it was necessary to obtain collections 

 from the same bed at as many localities as 

 time and opportunity permitted. The 

 identification of these beds had to be made 

 by other criteria than by means of spores. 

 This was not difficult in the Carbondale 

 group because the coal beds have been 

 traced almost continuously for many miles, 

 and it was possible to collect from the same 

 bed from localities in northern, western, 

 and southern Illinois. In some cases this 

 was also true for eastern Illinois. The 

 Caseyville and Tradewater coals and partic- 

 ularly the upper McLeansboro coals could 

 not be identified with equal certainty except 

 for relatively short distances. In general 

 it appears that tentative correlations that 

 have been made in the past were frequently 

 found not to possess the requirements of 

 stratigraphic relationship demanded by 

 standards imposed in these studies. When 

 there was uncertainty as to correctness of 

 correlation, even though general agreement 

 in fossil population existed, only the 

 probability of stratigraphic agreement was 

 suggested. Eventually the amount of evi- 

 dence was considerable and the validity of 

 the suggestions became increasingly more 

 probable. 



Some collections from a particular coal 

 bed were made at only one locality. It is 

 necessary to know what effect samples of a 

 particular coal bed from only one locality 

 will have in correlation. The available 

 evidence strongly indicates that the charac- 

 teristic spores are present in each macera- 

 tion, but in some cases the abundance ratios 

 vary in the same bed from two widely 

 separated geographic localities. Exceeding- 

 ly rare species of spores have not been used 

 as guide fossils and this tends to minimize 



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