26 GEOLOGY OF ILLINOIS. 



outcrop along the branch, nearly to the prairie level, showing the fol- 

 lowing succession of strata : 



Feet. 

 Shaly, micaceous sandstone, "becoming thicker-bedded and haider towards the bottom, and con- 

 taining broken plants '. 30 to 40 



Massive bro. sandstoDe, (main quarry rock) 8 to 10 



Ferruginous pebbly bed 3 



The massive brown sandstone quarried here is locally concretionary, 

 the concretions being much harder than other portions of the bed, and 

 afford a very durable stone. This sandstone, with the shales usually 

 associated with it, probably attains a maximum thickness of 60 to SO 

 feet, and fills the intervening space between coals Nos. 12 and 13 of the 

 general section. It has been penetrated in sinking wells on the prairie 

 at many places north and north-west of Eobinson. 



Law's coal bank, formerly known as Baton's bank, is on the S. W. 

 of the N. E. qr. of sec. 12, T. 7, B. 13. The coal is a double seam, 

 about three feet thick, with a parting of bituminous shale from two or 

 three inches to two feet in thickness. It is overlaid here by shale and 

 a hard, dark, ash-gray limestone, destitute of fossils. One mile up the 

 creek from this mine the coal is said to pass into a bituminous shale. 

 The coal obtained here is rather soft, and subject to a good deal of 

 waste in mining; but as the mine was not in operation when I visited 

 the locality, I had no opportunity of judging of its average quality. A 

 section of the creek bluff at the mine shows the following order : 



Ft. In. 



Gravelly clays of the drift 10 to 15 



Hard, dark ash-gray limestone 1 to 1 6 



Hard silicious shales, with nodules 6 



Coal, with shale parting— So. 13? 3 



A boring was made here by the proprietor, and a thicker seam was 

 reported to have been found some forty feet below ; but if this report 

 is correct, the sandstone usually intervening between coals Nos. 12 and 

 13 is here much below its average thickness, and no such coal is known 

 to outcrop in the county. However, local coals are sometimes developed 

 which only cover very limited areas, and this may be a case of that 

 kind. 



Four miles south-west of Eobinson a bed of hard, dark-gray bitumin- 

 ous limestone outcrops in the bed of Turkey creek, and has been quar- 

 ried for building stone, for which purpose it is but poorly adapted, as 

 it splits to fragments after a limited exposure to the elements. The 

 rock occurs in a single stratum about eighteen inches thick, overlaid by 

 a brown calcareous shale, filled with nodules of argillaceous limestone. 

 The shale contained numerous specimens of LophopJiyllum proliferum. 

 associated with joints of Grinoidw. The foundation stone for the court 

 house at Eobinson was obtained here. This limestone may overlay 

 a thin coal, but I could not learn that any seam had been found in 



