CASS AND MENARD COUNTIES. 169 



there appears a ledge of brownish sandstone, which extends along the river bank 

 about two hundred yards, with an elevation above the water of some six or eight 

 feet. This appears to replace the limestone over the middle coal, as it is stated 

 that that vein immediately underlies it, and was at one time worked at this point. 

 The rock appeared massive, or very irregularly bedded at this point, and seemed 

 to stand exposure well. 



The upper bed of coal is not at present worked, but the entrance to the old 

 drifts may be seen in several places along the Sangamon river bluffs, above Pe_ 

 tersburg. It does not outcrop near the village, but its position may be told by 

 these marks, and the clay shale which forms its roof appears at one or two 

 points up the ravine which opens out of the bluffs just above the woolen mills 

 on the southern outskirts of the town, and may be seen on close examination 

 at the mouths of some of the drifts. This shale is also exposed in other side 

 ravines farther up the stream, but the beds underlying the coal, and between it 

 and the middle seam, are only exposed at the Salem mills, some two miles above 

 Petersburg, on the west bank of the river. At this place, just below the mill- 

 dam, at the edge of the water, there is an outcrop of the middle coal, overlaid 

 by two feet or more of shaly, bluish limestone, and still above this, there is 

 exposed, in the almost perpendicular bank, nine or ten feet of light colored 

 shales, containing a few thin seams of clay and bands of iron ore. A little 

 farther up the road, and about ten feet higher in actual elevation, the upper 

 coal seam crops out of the bank on the roadside. It is here about sixteen 

 inches in thickness, and this is said to be pretty constantly the same in all places 

 where it has been worked. The thickness of the middle bed could not be well 

 ascertained by personal observation at the time of my visit, but it was stated to 

 me to be two or three feet. 



Following up the road south of the mills, the entrances to the disused drifts 

 along the bluffs at the side of the road, will show the position of the small 

 seam, though there are no good natural outcrops for some little distance. About 

 half a mile up this road, however, in the northwestern corner of section 36, 

 township 18, range 7, we find it again outcropping in the bed of a dry branch, 

 and a little farther up, the bottom and sides of the branch are composed of the 

 drab and brown, and in some parts nearly black, argillaceous shales, which form 

 its roof. This shale contains many concretions of ironstone, generally .lenticu- 

 lar in form, and sometimes of considerable size. Still farther up the ravine, 

 at Arnold's quarry, we find, above the shale, though the line of junction is no- 

 where visible, heavy beds of a light gray or bluish-gray limestone, exposed in 

 the hill sides to the hight of some thirty feet or more above the bed of the branch. 

 This limestone is quarried, both as a building stone and for the manufacture of 

 lime, and affords many fossils of the species Spirifer tineatus, Spirifcr camera- 

 tus, Athyris subtilita, Retzia mormoni, Rynclionella Osagensis, Productus Jongis- 

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