174 GEOLOGY OF ILLINOIS. 



slate in the roof, and the great thickness of the sandstone above are facts which 

 seem to slightly favor this view, but are, however, not conclusive. The absence 

 of exposures in the southwestern portion of Cass county, is to be regretted as 

 not affording the means of positively determining this question. 



This vein of coal is now actively worked at only one or two points in Cass 

 county, although it was formerly much more extensively mined along its out- 

 crop on the side of the bluffs of the Illinois and Sangamon rivers. The seam v 

 will average three feet in thickness, and is reported to be of fair quality, the 

 discontinuance of the most of the mining operations, was mainly due to the 

 small local demand, and the competition of other mines in the adjoining 

 counties on the Illinois river. 



In the eastern portion of this district, the lowest seam worked is No. 4 of 

 the general section, which will average in the different shafts and borings from 

 five to seven feet in thickness. Along the Sangamon river bottoms, at Peters- 

 burg and above, it has been met with at depths varying from seventy to eighty 

 feet. On the upland portions of the county, it has been reached but once, by 

 a boring at the depth of one hundred and seventy feet. This bed has every- 

 where a good roof of limestone and black slate, and' is generally easy to work, 

 although au occasional annoyance is met with in the shape of horse-backs, etc. 

 The coal is pretty uniformly of a good quality for fuel and steam purposes, al- 

 though the quality of some portions of the vein is sometimes injured for black- 

 smith's use by the presence of small quantities of sulphuret of iron. This is 

 the only seam of coal which is extensively worked at the present time. 



The next seam above this is No. 6 of the general section, which outcrops at 

 several points along the Sangamon river, in the vicinity of Petersburg, and is 

 also met with in one or two of the shafts at that place. A peculiarity of this 

 bed, which has prevented its having been worked to any extent, except along 

 its outcrop, is the tendency it has to run out, it ranging in thickness, within 

 short distances, from three feet to hardly as many inches. It is a softer and 

 less open burning coal than No. 4, and is therefore sometimes preferred to it 

 for blacksmith's use. 



Iron Ore. Mention has been made in the preceding pages of the concretions 

 of the carbonate of iron, which occur rather abundantly in the shales overlying 

 the small upper seam of coal near Petersburg. These, however, hardly seemed 

 to occur in any one place in sufficient abundance to continually supply an iron 

 furnace and render their reduction profitable. 



Building Stone. Probably the best material for building stone in this dis- 

 trict is the massively bedded, light gray limestone of the Coal Measures, which 

 is quarried on Rock creek, in the southern part of Menard county, and near 

 Salem, about two and one-half miles south of Petersburg. This may be ob- 

 tained in blocks of any convenient size, and appears to dress easily and weather 



