198 GEOLOGY OF ILLINOIS. 



. Cannel Coal in same Seam. 



Thickness of the bed from eight inches to one foot ; overlaid with black slate ; underlaid \vith four 

 feet of bituminous coal. No analysis of this coal has yet been made; but judging from its texture 

 and general appearance, it does not differ from the Wataga caunel coal. The coal is dull, hard, com- 

 pact ; fracture slightly conchoidal ; layers thick ; contains bright, yellow, vertical plates of sulphuret 

 of iron." 



NOTE. "While engaged during the past spring in examining the coal deposits of Rock Island, I was 

 induced -to extend my examinations into Henry county, in part to confirm observations previously 

 made in adjoining territory, and partly to satisfy myself as to the general development of our worka- 

 ble coal seams along the north-western confines of the Illinois coal field. 



Commencing at the north-west corner of the county, coal No. 1 of the Illinois river section i.s 

 opened and worked at various points in the bluffs of Rock and Green rivers, as at Cleveland and near 

 Colona, as shown by Mr. SHAW, in the sections given on the preceding pages, and it presents the, same 

 general characters here as at Carbon Cliff, Coal Valley, and other points in Rock Island county. It is 

 overlaid byapeculiar dark-gray silicious limestone, and its accompanying band of flint or chert, 

 that enables any one to identify it without difficulty. This seam is worked by the Messrs. Perry, at 

 Briar Bluff, near Green river, in Henry county, by a tunnel driven into the hill side. The coal is 

 somewhat variable in thickness, and is sometimes cut off altogether by what the miners term a 

 " horse-back." About forty feet below the coal the shaly limestones of the Hamilton group outcrop 

 but a short distance to the northward of the mines. A curious phenomenon was observed at these 

 mines in a remarkable geode-like cavern or pocket, occurring partly in the coal, and extending into 

 the fire clay beneath. The cavity was ovate in shape, and about ten feet long by five feet in width, 

 and two or three feet in depth, and surrounded by a solid crust. The inclosed cavity was tilled with 

 water and gas, and when the pick broke through the crust an explosion followed like the firing of a 

 blast. On breaking into the cavity it was found to be thickly set with magnificent crystals of dog- 

 tooth calcite, from six to eighteen inches in length, the points all directed towards the center of the 

 cavity like the crystals on the inner surface of a geode. Unfortunately many of these fine crystals 

 were broken up and destroyed in removing them ; but a few were preserved, and I was fortunate in 

 securing some of them for the State Cabinet. 



On the S.W. qr. of Sec. 21, T. 17, K. 1, coal seam No. 2 has been opened near the top of the bluff and 

 immediately under the boulder clay. The coal is 18 inches thick, and is overlaid by four or five fuet 

 of clay shale, forming but a poor roof. This was the first exposure of No. 2 that we met with in 

 Henry county. The coal was underlaid by a few feet of fire clay and clay shale, and not sufficiently 

 exposed to be accurately measured, which was followed by a bed of bluish-gray septaria two or three 

 feet thick, exactly like that found below the Colchester coal in McDonough county. This coal ap- 

 peared to be from 35 to 40 feet above No. 1 at this point. 



At the Mineral creek mines I found coal No. 1 worked in a shaft sixty feet in depth, and sunk in 

 the valley of a small creek, and about one hundred and fifty yards south-east of the shaft the same 

 coal outcrops seventy-five feet above it! level in the shaft. In a boring made at this point below the 

 coal they reported 7 feet of fire clay and 40 feet of shales, partly blue and partly gray, with a streak 

 of coal from two to four inches thick about half way to the bottom. Some layers of sandstone, and 

 one or more thin hands of iron ore, were passed through towards the bottom of the boring. 



At the Mauch-Chunck min^s, about six miles west of Geneseo, coal No. 1 is worked just above the 

 level of the creek by tunneling into the hill along its outcrop. It is here much thinner than it usually 

 occurs in this part of the county, being reported as varying in thickness from two feet to three feet 

 six inches. No. 2 is found here outcropping about forty feet above No. 1. A tunnel has been run into 

 it, and considerable coal taken out, though the seam is htre only from twelve to fifteen inches in 

 thickness. 



At Geneseo a coal seam crops out along the little run on the west side of the town, and is worked 

 by Mr. Maynard in a shaft sunk from a higher level near the outcrop. The beds passed through in 

 this shaft give the following section : 



Ft. lu. 



No. 1 Soil and drift clay 20 



No. 2 Hard rock, (probably limestone) 1 3 



No. 3 Sandstone 5 



No. 4 Bine shale 3 



No. 5 Coal 3 



No. 6 Hard dark shale 6 



No. 7 Hard rock (concretion ?) ..04 



