48 GEOLOGY OF ILLINOIS. 



Fossils are but seldom found in the Drift accumulations, and they consist 

 entirely of the remains of mammalia ; no shells, either marine or fresh water, 

 having yet been found in them in this State. 



Carboniferous System. 



All the paleozoic rocks that appear above the surface in this county, belong to 

 this system, and comprise the lower portion of the Coal Measures, and the whole 

 series of the Lower Carboniferous limestones, except the Chester series, and 

 the lower part of the Kinderhook group. 



Coal Measures. This term is applied to that portion of the Carboniferous 

 system that contains the workable seams of coal, and comprises shales, sand- 

 stones, bituminous slates, and thin bands of limestone, with seams of coal and 

 the fire clays that underlie them. The whole thickness of these strata in this 

 county, probably nowhere exceed about one hundred and twenty feet, and they 

 include the three lower coal seams, and the strata associated with them. The 

 greatest development of this formation is in the northeast part of the county, 

 on Little Missouri creek, where there is an exposure of some fifty or sixty feet 

 of shales with two thin beds of limestone, above No. 2 coal, which is worked at 

 different points in the valley of the creek. 



The following section will show the general arrangement and thickness of the 

 coal strata, as they are developed in this county : 



FT. IN. 



Hard, gray, nodular limestone 3 to 6 



Sandy shale and sandstone 25 " 30 



Black shale 2 " 4 



Coal, No. 3, sometimes wanting 1 8 



Fireclay 2 " 3 



Clay shale 25 " 30 



Coal, No. 2 2 " 3 



Fire clay and clay shale. 4 " 10 



Gray nodular limestone 4 " 5 



Shale 10 " 15 



Bituminous slate 1 " 3 



Coal, No. 1 li" 2 



Shale and sandstone 20 " 30 



The middle coal seam in the above section, (No. 2,) is the most regular in 

 its development, and furnishes altogether the best coal in the county. It out- 

 crops on the south fork of Bear creek, and is worked by Mr. Ferguson, on the 

 northeast quarter of section 17, township 1 north, range 6 west. The coal at 

 this point ranges from two to three feet in thickness, and is of good quality, 

 being generally quite free from the bi-sulphuret of iron. The roof is a bluish 

 clay shale, of which, about fifteen feet in thickness is exposed at the mine, 



