328 7 GEOLOGY OF OHIO. 
mine cannot be laid out at all. Moreover, a considerable part of hill 
coal along its line of outcrop is so largely impregnated with iron rust and 
earthy matter, as to render it unfit for market. In deep shaft mines, 
which discharge a great flow of water, the advantages are in favor of 
drift mining, but we have neither deep nor wet mines in Ohio. 
THE MANNER OF MINING. 
In districts in which coal seams about to be developed are 
level-free, the manner of opening mines is simple and inexpensive. 
The coal is usually exposed at some point on the hill-side, and is readily 
distinguished by a dark colored streak on the clay, called the coal 
“blossom” or “outcrop.” As the blossom is followed into the hill it 
gradually hardens into coal. For some yards, sometimes for many 
yards, the coal is soft, dead and rusty. ‘This is called crop coal, and 
cannot be shipped. Ifthe front of the hill in which the mine is opened 
is bold and steep, the coal soon becomes compact and bright, and fit for 
commercial use; but if the hill is retreating, and the mine is opened 
near the top, the entries may be pushed from 50 to 100 yards before 
merchantable coal is met. On lands where the cover is light, say 30 
or 40 feet, and is mainly composed of alluvial matter, only a few feet of 
shale forming the immediate cover of the seam, the coal is often so 
tender and earthy as to be worthless. Under such conditions the roof 
is never good. 
All drift mines require to be timbered for some distance from the 
mouth. The timbers, which are made out of hewn or sawed wood, are 
usually 8 by 10 inches in size, their length being governed by the height 
of the seam. The bents are sometimes placed close together, but are 
generally set about 23 to 3 feet apart, the intermediate space being 
filled with 2-inch plank. The leg of each bent of timbers slants inward 
about 1 foot in 6. If the bottom of the mine is wet, cross-sills are laid 
under each bent to keep them from sinking. 
The mine is usually made from 8 to 10 feet wide, and the timbering 
is carried forward until the roof becomes so firm that it will safely stand 
of its own accord. | 
The point usually selected for opening is as near the southeast line 
of the mining property as may be practicable, so as to extend the work- 
ings to the north and west, along the rise of the strata, to facilitate 
hauling and draining, For 100 to 200 feet the coal usually dips from 
