MIDDLE DEVONIAN COAL IN ILLINOIS 



50 MILES 



a dense, light to dark gray limestone 

 near Davenport, Iowa. The Upper 

 Davenport was later included in the 

 Cedar Valley Limestone, whereas the 

 Lower Davenport was changed to simply 

 the Davenport Limestone Member. 



In a comprehensive discussion 

 of the stratigraphic relationships, no- 

 menclature, and paleontology of the 

 Devonian rocks in the north-central 

 United States, Collinson et al. (1967) 

 stated that the Wapsipinicon Limestone 

 extends from Iowa into northwestern Illi- 

 nois where it wedges out onto the Sanga- 

 mon Arch. They tentatively correlated 

 the Wapsipinicon with the lower Lingle 

 and Grand Tower Formations of central 

 Illinois. James (1968) and Collinson 

 and James (1968), in a more detailed 

 stratigraphic and paleontological in- 

 vestigation of the Middle Devonian car- 

 bonates, traced the Wapsipinicon as far 

 as DeWitt County, into the area of the 

 coal occurrence where it overlaps onto 

 the Sangamon Arch. James (1968, pi. 3) 

 constructed a paleoecological map of 

 the top of the Wapsipinicon in Illinois 

 that shows the distribution of various 

 lithologies, including the coal and 

 coaly shale. 



Text fig. 1 - Locations of samples 1, 2, 

 and 3 and their positions relative to 

 the Sangamon Arch during the deposi- 

 tion of the Devonian coal in Illinois. 



PETROGRAPHIC DESCRIPTION 

 OF THE SAMPLES 



The microstructure of the coal is 

 characterized by different degrees of pre- 

 ferred particle orientation. Some horizons 

 are well laminated, whereas others lack any preferred particle orientation. The 

 percentage of spores and other organic matter increases with the degree of orienta- 

 tion. The well stratified portions contain between 40 and 75 volume percent organic 

 matter (pi. 1, fig. 2). The layers that lack internal orientation of the particles 

 contain only about 30 volume percent coaly material, which is made up almost 

 entirely of vitrinite. 



Sample no. 1 (text figs. 1 and 2, and table 1) represents the best develop- 

 ment of coal in the three cored sections (pi. 1, fig. 1). It occurs 14 feet (4.3 m) 

 below the top of the Wapsipinicon Limestone. The coal, which is a little more 

 than one-half inch thick, is dull, fine grained, fractures conchoidally, and has a 

 somewhat canneloid appearance. It is cut by several highly polished and slicken- 

 sided horizontal and high-angle planes. The contact with the limestone is irregular 

 and in part almost vertical (pi. 1, fig. 1). The limestone is medium to dark gray, 



