316 GEOLOGY OF ILLINOIS. 



found. ' It is associated with Bellerophon carbonaria, B. nodocarinatus, 

 B. Stevensianus, Pleurotomaria Grayrillensis, Schizodits, Platyostoma Pe- 

 oriense, Pinna per -acuta ? and Petalodus destructor. If we divide the Coal 

 Measures at all in this State, this limestone may very properly be 

 included in the upper division, as it contains at least three or four 

 species of fossils that we have not seen in any lower horizon. This 

 limestone will probably be found in the bed of the Sangamon river 

 somewhere in Springfield township, unless it has been swept away by 

 erosion. 



In the eastern portion of the county rock exposures are rarely met 

 with, and the few that are to be seen are mainly shaly sandstones and 

 sandy and argillaceous shales. At the mouth of Clear creek some beds 

 of shaly sandstone are found, which are probably the equivalents of the 

 soft shaly sandstone forming the top of the bluff on the east side of the 

 Sangamon, near Hewlett. 



There are probably from seventy-five to a hundred feet of shales and 

 sandstone, belonging above the limestones on Sugar creek, which out- 

 crop along the breaks of the Sangamon between Howlett and the east 

 line of the county, but the exposures are so local and widely separated, 

 that no satisfactory section can be made from surface exposures. They 

 include a thin seam of coal, which, in the boring at Decatur, was twelve 

 to fifteen inches thick, and about 250 feet below the surface. 



Commencing at the west line of the county, the main coal worked in 

 - the shafts in Sangamon and Macoupin counties, which I believe to be 

 No. 5 of the general section of our Illinois coals, is found at the depth 

 of 120 to 150 feet below the general prairie level, and it dips eastwardly 

 at the rate of about six feet to the mile, and in the central portions of 

 the county it will be found from 200 to 250 feet below the general level, 

 and in the eastern portion, from 300 to 400 feet, to which we may add 

 the additional surface elevation of the eastern part of the county. No 

 borings have yet been made at any of the coal shafts to determine how 

 many of the seams underlaying No. 5 are developed in this portion of 

 the State to a sufficient thickness to be profitably mined, but it is prob- 

 able there are three or four underlaying seams, that will range from two 

 to four feet in thickness. The supply from No. 5, however, is so great, 

 that it will probably be many years before any serious attempts will be 

 made to mine the. lower seams in this county. At every point in the 

 county where a reliable boring has been made, or a shaft sunk to the 

 horizon of this coal, it has been found well developed, being usually 

 from five to seven feet in thickness, with an excellent roof of bitumin- 

 ous shale and limestone. None of the shafts in this county are troubled 

 with water, and in most of the mines the rooms are as dry as an ordin- 

 ary underground cellar. 



