SPORE DISTRIBUTION — CASEYVILLE 



77 



100 feet of rocks at the top of the Chester in 

 Illinois are still unknown. This informa- 

 tion, when available, could possibly change 

 or soften the apparently abrupt distinction 

 between uppermost Mississippian and low- 

 ermost Pennsylvanian assemblages (text 

 fig. 7) . 



Miscellaneous Samples of Chester Age 



Of two samples from two coaly streaks in 

 the upper part of the Stony Gap Sandstone 

 at Pounds Gap, Letcher County, Kentucky, 

 one (maceration 911) contained numerous 

 fertile and abortive spores of Cystosporites 

 giganteus and a few megaspores of Triletes 

 subpilosus forma major, but the other 

 (maceration 912) was barren of mega- 

 spores. 



A sample from a coal (maceration 913) 

 in shales of the Pennington Formation, 

 Cumberland Gap, Bell County, Kentucky, 

 was barren of megaspores. 



Summary 



Although megaspores may occur in great 

 numbers in rocks of Chester age, very few 

 types are represented. The assemblages as 

 a whole are dominated by spinose lagenicu- 

 late and fibrous-coated spores, representing, 

 among the heterosporous plants, a domi- 

 nant lepidocarp-lepidodendrid flora. 



Three genera identified from the Chester 

 Series also are represented in Pennsylvanian 

 coals; four other genera first occur in the 

 Pennsylvanian (text fig. 8) . 



Spores of Didymosporites are known only 

 from the lower part of the Chester Series. 

 Within the genus Triletes four species are 

 restricted to rocks of Chester age, whereas 

 eight species are first represented in the 

 Caseyville Group of Pennsylvanian age. 

 Three other species are represented in both 

 the Chester and Caseyville rocks, but varie- 

 tal forms of only two can be distinguished 

 (text fig. 7) . Therefore, of 25 taxonomic 

 entities that are distinguishable (text fig. 

 7) , only two are common to upper Missis- 

 sippian and Pennsylvanian rocks. 



Pennsylvanian System 



In late Chester time a long period of sub- 

 aerial erosion followed uplift and with- 



drawal of the sea. A second erosion cycle, 

 initiated by a subsequent uplift, resulted 

 in the incision of deep channels in the pene- 

 plain surface (Siever, 1951) so that in 

 southern Illinois Pennsylvanian rocks rest 

 on the eroded surfaces of rocks of upper 

 Chester age, but northward they rest on 

 successively older rocks as far down as the 

 St. Peter Sandstone of Ordovician age. This 

 unconformity is one of the most important 

 within the Paleozoic era of the east-central 

 United States (Wanless, 1955) . 



The Pennsylvanian deposits in the East- 

 ern Interior Coal Basin are noted for their 

 arrangement in repeated successions of rock 

 types designated as cyclothems by Weller 

 (1930) and Wanless and Weller (1932). 

 The rocks are principally shales and fine- 

 grained sandstones with many beds of lime- 

 stone, black shale, coal, and underclay. In 

 Edwards County, Illinois, and in parts of 

 surrounding counties (Workman, Swann, 

 and Atherton, 1950; Wanless, 1955), the 

 total thickness attains a maximum of about 

 2500 feet. 



The Pennsylvanian succession has been 

 divided into four groups, from oldest to 

 youngest: Caseyville, Tradewater, Carbon- 

 dale, McLeansboro. Cady (1952) stated 

 that there are 40 to 50 coals in this succes- 

 sion. The coals that are more important 

 commercially are within a section that oc- 

 cupies the upper 200 feet of the Tradewater 

 Group, the Carbondale Group, and the 

 lower 100 feet of the McLeansboro Group. 

 Most of the Pennsylvanian samples used in 

 this investigation were from coals, and, ex- 

 cept for a few principally of Caseyville age, 

 were from localities within Illinois. 



CASEYVILLE GROUP 



The rocks of the Caseyville Group, the 

 oldest group of Pennsylvanian strata in 

 Illinois, include all those below the base of 

 the Grindstaff Sandstone. These rocks, up 

 to 470 feet thick (Cady, 1952), are charac- 

 terized by massive cross-bedded sandstones 

 commonly containing quartz pebbles, by 

 somewhat thin discontinuous coals, and by 

 a paucity of limestone. The coals are of 

 only slight economic interest except in 

 southeastern Jackson and northeastern 



