GEOLOGY OF ILLINOIS. 



line, in Jersey county, and their outcrop Las been fully described in 

 the report on that county in Vol. Ill, p. 108, of these reports. In that 

 vicinity these two coals only average from three to four feet in thick- 

 ness at the outcrop, but No. 5 evidently thickens to the eastward, in 

 the direction of the dip, as in one of the shafts at Bunker Hill it aver- 

 ages about six feet, and about the same or a little more in the shafts at 

 Staunton. It is probable that Macoupin creek, in its course through 

 township 9 north, range 9 west, may expose some of the shales and 

 sandstones below coal No. 4, but from the wide bottoms and limited 

 exposures of the beds in the creek bluffs, we are unable to decide this 

 point. 



In dividing the Coal Measures into an upper and lower division, as 

 seems desirable on many accounts, I am inclined to regard the heavy 

 bed of sandstone and shale, No. 19 of the Virden shaft section, as about 

 the proper horizon where the division should be made, as the beds 

 underlaying this sandstone contain all the heavy beds of coal worked 

 at the present time in this State. There is however one of the upper 

 seams outcropping in some of the eastern counties of the State, that 

 attains locally a thickness of about 3 feet, and is some 300 feet higher 

 in the Measures than this sandstone. Nevertheless, there appears to 

 be a decided change in the coal-forming conditions after the deposit of 

 this sandstone, resulting in thin seams of coal interstratified with cal- 

 careous shales and numerous beds of limestone, indicating a more gen- 

 eral and long continued submergence of the surface below the ocean's 

 level, and comparatively short periods of emergence, and of true plant- 

 producing conditions. This sandstone is probably the equivalent of 

 the Mahoniug and Anvil Eock sandstones of Kentucky, the latter being 

 considered in the Kentucky section as the upper boundary of the work- 

 able coals of that State. These sandstones, as I have attempted to 

 show in the chapter on the general distribution of the coal in this State, 

 in Vol. Ill, p. 7, are most probably one and the same bed, which, at 

 widely separated exposures, were taken to be two distinct sandstones, 

 occupying entirely different stratigraphical positions. 



The seven coals underlaying this sandstone range from three to eight 

 feet in thickness, except the upper one immediately below it, which, at 

 the exposures seen in this county, is scarcely developed above one foot 

 in thickness, though at other localities, as in Fulton county, it ranges 

 from twenty to thirty inches, and affords a coal of excellent quality. 

 The coals above the sandstone in this county are Nos. 8, 9, 10 and 11, 

 all of which are too thin to be of any economical value. No. 8, which, 

 in the Virden shaft (No. 18), is only ten inches thick, is probably iden- 

 tical with the eighteen-inch coal outcropping in the vicinity of Spring- 

 field, and which, on the Sangamon at Howlet, is two feet in thickness, 



