DEVELOPMENT OF PALEOBOTANY IN THE ILLINOIS BASIN 25 



Abundant 

 reported 



Pig. 4 



Coal-ball localities 

 nois Basin. 



in the Illi- 



Plant lists published by Noe, his 

 students, and other new paleobotanists 

 interested in coal-ball plants soon es- 

 tablished the general nature of the coal- 

 ball floras of the middle and upper part 

 of the Pennsylvanian of the Illinois Ba- 

 sin. Lower vascular plants were gener- 

 ally predominant and included large ar- 

 borescent lycopods, calamites, Psar- 

 onius ferns, smaller seed ferns, and rel- 

 atively few cordaites. The fairly com- 

 mon, smaller plants included Spheno- 

 phyllum, Selaginella, Botryopteris 3 Zy- 

 gopterisj and Anaohoropteris . 



Nature and Occurrence of Coal Balls 



Coal balls are spherical to irreg- 

 ular masses of fossilized peat that oc- 

 cur in coal seams. Plant structures in 

 the peat survived coalification of the 

 surrounding material and are remarkably 

 well preserved. The plant material is im- 

 pregnated with calcite, dolomite, sid- 

 erite, pyrite, or silica . Calcareous, 

 dolomitic, and pyritic coal balls are restricted to seams formed under marine influence. 



One of the questions most often asked about coal balls is how they are form- 

 ed. It is a complex problem still under investigation by geologically oriented pa- 

 leobotanists and geologists. Many answers have been offered; the first from the 

 United States was by Feliciano (1924). Kindle (1934), Evans and Amos (1961), 

 Weber and Keith (1962), and Cross (1969) also contributed answers. Perhaps the 

 best picture of coal- ball origin can be found in the outstanding publications of 

 Stopes and Watson (1909), Teichmuller (1952), and Mamay and Yochelson (1962). 

 The mineralogy and petrography of coal balls from Illinois and other areas are now 

 being investigated by Prasada Rao. 



A likely explanation, derived from various publications, for the origin of 

 calcareous coal balls is that marine calcareous material was transported into the 

 peat, either in solution or as calcareous ooze. The calcareous material was then 

 dissolved by the acid in the water of the peat bog. Slight changes in the pH value, 

 usually triggered by the carbonates themselves or by the incoming sea water, al- 

 lowed the carbonates to flocculate as a gel. Later, devitrification resulted in 

 needle-shaped crystals, often spherulitically arranged. 



Early discoveries of coal balls in the basin included those from an unnamed 

 coal a few feet above the Minshall Coal Member of Indiana near Cayuga, from the 

 Harrisburg (No. 5 Coal)near Harrisburg, from the No. 9 Coal at Sturgis, Kentucky, 

 from the Herrin (No . 6) Coal, from the Danville (No . 7) Coal near Danville, and 

 from the Calhoun Coal of Richland County (Feliciano, 1924; Noe, 1925a) (fig. 4). 



Although coal balls were known from all six of these coals by 1930, the se- 

 quence of discovery and the quality and abundance of coal balls in each coal led 

 to emphasis on plants from the Harrisburg Coal first, on those from the Danville 

 Coal next, on those from the Calhoun Coal third, and later and quite extensively 



