170 GEOLOGY OF ILLINOIS. 



pinus, and others. The exposures of both this limestone and the underlying 

 shales, are not such as to allow any very exact estimate of their respective 

 thicknesses. The limestone, however, will probably not exceed twenty or thir- 

 ty feet, and the shale fifteen or twenty feet in total thickness. 



On the Sangamon river above the Salem mills, there are no very good expo- 

 sures above high water mark, though beds of rock are said to form the bottom 

 of the stream at one or two points. A coal shaft, however, which was sunk 

 on the land of Mr. Sampson, in the southeast quarter of section 32, township 

 18, range 6, affords a section of all the beds, from the top of the upper seam 

 of coal to the under clay of the lower and largest bed. The total depth of the 

 shaft is a little over ninety feet, and the strata were passed through in the fol- 

 lowing order, as reported to me : 



FEET. IN. 



1. Surface soil and blue clay 14 



2. Black slate or shale 1 



3. Coal 1 3 



4. Fire clay and shale 17 3 



5. Hard limestone. 4 



6. Coal 2 6 



7. Fire clay and shale (very hard) 39 



8. Black slate 1 



9. Coal 6 4 



10. Fire clay, penetrated in sump .* 5 



It will be observed that, in this section the limestone, which generally is 

 found just above the roof slate of the lower coal, is missing. This, however, 

 is probably only a local peculiarity. 



Another point along the bluffs of the Sangamon, where rock is said to occur, 

 is in the northwestern part of section 15, township 17, range 6, on the land of 

 Mr. A. Hale, where it is stated that limestone was quarried out in former times. 

 I visited the excavation, but the rock was not visible above the rubbish, and 

 judging from the chips, I made out the rock to be the same in appearance and 

 fossils as that in Arnold's quarry, near Salem. The only doubt is, whether this 

 may not have been merely a large detached mass, imbedded in Drift, like many 

 in this vicinity. 



In the northeast quarter of section 19, township 18, range 5, on the head- 

 waters of Indian creek, there appears in the banks and beds of the stream, for 

 about two hundred yards, a bed of light colored, nearly white, limestone, which 

 seems to be almost entirely made up of crinoidal stems, no other fossils being 

 observed. Half a mile or more below this, on the land of Mr. T. Kincaid, in 

 the northeast quarter of section 24, township 18, range 6, the limestone again 

 appears, and has been quarried to the depth of about seven feet. It is here 



