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 erowth 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 first 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 blackband 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. f 
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 slepe 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 buff color, and it is 
frequently referred to in our notes and reports as the Buff Limestone. 
The greatest development of this stratum that has come under my ob- 
servation is in the hill above New Cumberland, on the eastside 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 
