160 GEOLOGY OF ILLINOIS. 



St. Louis Limestone. The outcrops of this formation are confined to the base 

 of the bluffs, along the eastern edge of the Illinois bottoms in this county. In 

 lithological characters, it is also rather variable, consisting of reddish and light 

 colored sandstones, and a hard, impure, reddish, calcareous rock, which appears 

 in one or two places. It nowhere presents such a development as may be met 

 with farther south, and disappears entirely before reaching the northern limits 

 of the county. The most northern exposure observed, was in the southwest 

 corner of section 19, township 16, range 12, on the land of Mr. Chamberlain, 

 where I observed a light gray limestone on the sides of the bluff road, and a lit- 

 tle higher up on the side of the bluff, large, tumbling masses of a light colored 

 sandstone. About a quarter of a mile below this point, ledges of a reddish, 

 splintering, calcareous sand rock, appear in the side of the bluffs, and have been 

 somewhat quarried. 



Passing still further to the south and west, along the bluff road, we see at 

 various points, a light reddish, shaly sandstone, appearing in the ditches along- 

 side of the road, and in the bottoms of some of the small ravines, which come 

 down through the bluffs. Mention has already been made, in the earlier part 

 of this chapter, of a reddish sandstone occurring in heavy ledges up in the ra- 

 vines of Coon run, which may, possibly, belong to this formation, but more 

 probably to the Coal Measures. About half a mile north of the southern line 

 of the county, in the western part of section 36, there is a small quarry on the 

 edge of the bottom, in a rather coarser grained, light colored sandstone, which 

 has been excavated to the depth of about four feet. In none of the exposures 

 of the rocks of this age in Morgan county, were any good fossils obtained, but 

 ledges of rock containing some of the characteristic fossils of this group in tole- 

 rable abundance, occur a short distance over the boundary in Scott county. 



FEET. IN. 



Gray, sandy shale 12 



Clay shale with iron bands 6 



Conglomerate 2 6 



Gray shale 14 



Limestone 6 



Black shale with concretions of septaria 4 



Coal 3 



Fire clay, not passed through 1 6 



The fire clay passes downward into a very hard, arenaceous rock, filled with Stigmaria. The 

 slaty, black shale of the roof contains lAngula umAonata, Discina nitida, Aviculopeden rectala- 

 terarea, and Monotis? gregaria. .The concretions of septaria are veined with selenite. From 

 the appearance of the coal and the beds with which it is associated, I am inclined to regard 

 it as probably the equivalent of coal No. 3 of the section in Fulton county. A. H. W. 



