6 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 500 



silt and clay occur. The sandstones are gray, veil sorted, and composed 

 of quartz; the shale lenses are gray. Where -weathered, the shales, silts 

 and sandstones become ochre to rust brown. The bases of some sandstone 

 beds are conglomeratic with clay pebbles dominating. This lithology, 

 together with the irregular and wavy bedding of the coarse cross-strati- 

 fication, indicates deposition in rapidly moving water. Further indica- 

 tions of deposition in such water are the twisted and distorted plant 

 fossils which often cross bedding planes. That the plants were brought 

 in by fast-moving water is also indicated by the fact that they are most 

 common in the coarser beds. 



Overlying the fossil-bearing strata is a rust-colored shale. It 

 overlaps the top of the Salem and caps the hill between the two collecting 

 localities. Its thickness and exact stratigraphic relationship are not 

 known; however, it probably underlies the Babylon Sandstone Member of 

 the Abbott Formation. The Babylon Sandstone in the report area is approx- 

 imately h meters thick, although elsewhere it is as much as 8 meters 

 thick. It is composed almost entirely of medium to coarse quartz grains. 

 For the most part, the sandstone is light gray to yellowish gray, but 

 the weathered surface may be iron-stained a reddish brown. The upper 

 part is thick and irregularly bedded to massive, and contains Stigmaria 

 and Lepidodendron impressions. The lower part is cross bedded and con- 

 tains carbonaceous partings. To the northeast, the sandstone intertongues 

 with shale. 



Overlying the sandstone is approximately 30 cm of underclay and 

 shale, light near the top and darker and sandier near the base. A thin 

 coal is exposed where a road crosses a creek about 300 m south of the 

 collecting localities. The coal ranges in thickness from ^5 cm to only 

 8 cm. The thinning is apparently the result of post-lithif ication chan- 

 neling, as the base of the coal is even and the upper contact very ir- 

 regular. The coal has been tentatively identified as the Pope Creek 

 Coal Member of the Abbott Formation. 



The hiatus between the Mississippian and Pennsylvanian beds is 

 apparently quite long in Brown County. The St. Louis Limestone is the 

 youngest Mississippian unit preserved, and the entire Chesterian Series 

 is missing. The first widespread deposit of Pennsylvanian age is the 

 Babylon Sandstone Member of the Abbott Formation. Thus the Caseyville 

 is represented only by the plant-bearing beds. 



The St. Louis Limestone has been tentatively correlated with the 

 cu III a in Europe (Collinson, Scott, and Rexroad, 1962). The Babylon 

 Sandstone is of Westphalian B age. Thus the upper part of the Visean, 

 the entire Namurian, and the Westphalian A are missing between these two 

 units. This gap represents a time span of 10 to 20 million years (Fran- 

 cis and Woodland, 196k), The plant-bearing strata could have been de- 

 posited any time during that interval. Determination of the age of the 

 flora is thus crucial for the dating of these beds. 



LYCOPSIDS 



Lepidodendron wortheni Lesquereux 



Text fig. l+A; pi. 1, fig. 1 



The single specimen of Lepidodendron from the Spencer Farm lo- 

 calities consists of nine leaf cushions in an area 3.5 by 1.5 cm. The 



