76 GEOLOGY OF OHIO. 



the mountain ore is found to thicken in one direction, the blackband in 

 the other, showing that the calcareous deposit extended from a lower 

 level — a deeper portion of the basin — up over the carbonaceous mud 

 which had previously partly filled it. From what we know of the forma- 

 tion of coal we can positively assert that Coal No. 7 accumulated in a 

 marsh, precisely as peat now forms by a growth of vegetation in the 

 open air; in other words, that it was practically a land surface. That 

 this peat bed was subsequently covered with shale and limestone proves 

 that it was depressed and covered, first with shallow water, in which 

 carbonaceous mud and clay were firtt deposited, the former deriving 

 its organic material from the disintegrated peat. As the subsidence 

 progressed the water in the basin became clear enough to permit the 

 formation of limestone, which was naturally purest and thickest in the 

 deeper places, and thinned away to an edge on the muddy shallows. 



It has been reported that the blackbanld ore has in a few places been 

 found to reach a thickness of twenty feet, but no such development of 

 the deposit has come under my observation. It usually ranges from 

 three to six feet, but at the mines of Mr. A. Wilhelmi, in Auburn town- 

 ship, and in the Patterson ore-bank, near Port Washington— now owned 

 by the Glasgow Port Washington Iron Company — I have seen ten and 

 even twelve feet of solid ore. 



The limestone ore shows equal irregularities of thickness. At Wil- 

 helmi's mine, in one of the old openings, it is seen increasing from noth- 

 ing to three feet in thickness, running down a slope of blackband ore, 

 and practically taking its place. Throughout the area occupied by the 

 limestone, that is, over parts of Stark, Carroll, and much of Tuscarawas, 

 the limestone is met with at intervals, having, where present, a thick- 

 ness of four to five feet. Even where not forming an iron ore, it contains 

 so much iron as to assume, in weathering, a decided bufi color, and it is 

 frequently referred to in our notes and reports as the Bufi' Limestone. 

 The greatest development of this stratum that has come under my ob- 

 servation is in the hill above New Cumberland, on the east side of the 

 Conotton valley. Here it is apparently nearly twenty feet in thickness; 

 as usual, nodular in structure, and containing so much iron that some of 

 the nodules are good mountain ore. 



The iron found at this horizon, in the form of blackband, or mountain 

 ore, where present in full force, constitutes by far the richest ore deposit 

 of the State. Tracts of many acres might be specified underlain by a 

 continuous sheet of blackband, eight feet in thickness, and, since this 

 contains twenty-five per cent, of metallic iron, it is equivalent to a sheet 

 of cast-iron over two feet in thickness of equal extent. The inhabitants 



