CASS AND MENARD COUNTIES. 171 



somewhat different, the upper five feet in the quarry being of a grayish, heavi- 

 ly-bedded limestone, containing very few fossils. A section of the quarry 

 would be nearly as follows : 



FEET. IN. 



1. Heavy bedded, gray limestone 5 



2. Dark colored, somewhat shaly beds 1 6 



3. Dark colored, argillaceous shale, containing Hemipronites crassus, etc 6 



4. Hard, pyritous band, with a trace of coal 1 



5. Whitish fire clay, only penetrated 8 



Numbers 4 awd 5 of this section, are not to be seen in this quarry without 

 special excavation, and numbers 1 and 2 appear to graduate into each other at 

 some points. 



Below this for about a quarter of a mile, the limestone is met with by dig- 

 ging into the banks, and outcrops at one point in the side of the branch, about 

 one hundred and fifty yards below the quarry. The rock there is somewhat 

 different from that before described, being a very light colored, nearly white, 

 thinly and irregularly bedded limestone, containing Spirifer lineatus, Athyris 

 subtitita, and a few other species, in considerable abundance. 



The remaining exposures in the southern part of Menard county occurs in 

 the southern parts of sections 13, 14 and 15, township 17, range 7, along the 

 banks of Rock creek. The easternmost of these, occurs in the southeast cor- 

 ner of section 13, a little west of the Springfield road, where a thickness of a 

 few feet of light colored shale appears in a field on the bank of the creek. About 

 three-fourths of a mile above this on the stream, and nearly due west, we came 

 to the first of the limestone quarries, which continue to appear at intervals for 

 upwards of a mile above this along the creek. The stone which is quarried 

 here is a gray or bluish-gray fossiliferous limestone, occurring in rather heavy 

 beds in the bed of the creek, and in the sides of the bluffs along its course. 

 In one or two places I noticed from one to two or three feet of brownish shaly 

 sandstone immediately above, and resting upon the limestone. It seems to me 

 probable that this limestone may be identical with that at Arnold's quarry, 

 near Salem, and in that case it will probably be found to underlie the Drift 

 deposits over a considerable area in the southern part of Menard county. Its 

 thickness at this point could not be well ascertained, as at no one point is there 

 exposed more than a few feet, but from the difference of level of the different 

 outcrops and workings, the beds being apparently horizontal or nearly so, 1 

 should judge that it is not less here than at Arnold's, at least twenty feet, and 

 perhaps more. 



North of Petersburg, in Menard county, there are comparatively few out- 

 crops, or artificial exposures, borings, etc. At the eastern extremity of the 

 wagon bridge over the Sangamon, near the brewery, there is a slight exposure 



