File:Penn carbondale 4-20.jpg
Figure 4-20. Field sketch by W.J. Nelson (1983) illustrating apparent splitting of the Colchester Coal. Underclay and lower splits of coal are at the lower right. Separating the lower and upper coal benches is gray, weakly laminated siltstone that resembles normal Francis Creek Shale. No underclay or rooted zone was observed below the upper coal bench. This feature may have formed when the bulk of the Colchester peat deposit was rafted during early stages of Francis Creek deposition. Sandstone overlying the coal underwent compressional folding and shearing prior to lithification, possibly as a result of sediment compaction. Width of view: ~75 feet (23 m) laterally and 25 feet (7.6 m) vertically. Locality: Stream bank in Argyle Lake State Park, SE1/4 NE1/4 SW1/4, sec. 31, T 6 N, R 3 W, McDonough County. © University of Illinois Board of Trustees.
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