346 GEOLOGY OF OHIO. 
EXAMPLES OF Goop MINING PRACTICE. 
The manner of mining in some of the older and more important 
regions of the State, where good practice generally prevails, will now 
be briefly described. 
The system of mining in the Mahoning Valley, owing to the 
conditions under which the coal was deposited, is peculiar and 
curious. The coal, which is the lower bed of the State series, is subject 
to sudden changes of level, and is found disposed in long, narrow, and 
serpentine basins or troughs. Generally these basins are separated from 
each other by large areas of barren ground, in which the coal is geo- 
logically due, but was never deposited ; occasionally two or more of the 
basins run along side of each other in nearly parallel lines, the coal 
extending from one basin to another in the form of an anticlinal arch, 
without breaking its continuity, though becoming very thin on the high 
lands of the old coal plain. The low ground in the coal bed is called 
a swamp by the miners. Owing to the structure of these swamps, the 
workings cannot be laid out with any degree of symmetry, and peculiar 
mining skill is required to guide and direct the subterranean excava- 
tions. The line of direction of the swamps is very sinuous, resembling 
the bed of a rivulet, and the main galleries of the mines have to be 
opened in these swamps, following their lines of direction through all 
their sinuosities, in order to drain the workings of water. 
The mines are all shaft openings, ranging in depth from 50 to 250 
feet; the stratum overlying the coal is a hard and compact gray shale ; 
the floor is a firm, hard, sandy fire-clay, and the coal seam itself is a 
hard, firm, compact, block coal. When to these conditions are added 
the fact that the basins are generally quite narrow, seldom excee‘ling a 
few hundred yards in width, small pillars suffice for the support of the 
overlying rocks. The main entries of the mine, which are driven from 
8 to 9 feet in width, follow the swamp, as I have said, wherever it may 
lead, the line of direction of the swamp being usually southwest. At 
intervals of 160 yards, branch entries are driven on the butts of the 
coal, and the rooms, which are usually 10 to 12 yards wide, are worked 
at right angles from the butt entries; pillars, two to three yards in 
thickness, which are cut through every few yards for air, being left 
between rooms to support the roof. 
All the entries of the mines, face and butt alike, are driven in the 
swamp when it is practical to do so; as the seam of coal is seldom high 
