332 GEOLOGY OF OHIO. 
Mahoning ‘Valley district, which will be found in another part of this 
chapter, a brief sketch of it will be given. 
There are a number of methods or systems of laying out the work- 
ings of mines in use, according to the varying conditions which are met 
in the several mining districts, as, for example, the thickness of the 
overlying strata, the character of the roof as to hardness and softness, 
the nature and thickness of the underlying fire-clay, the ability of the 
coal seam to resist pressure, ete. Suitable modifications of all the 
English systems are practiced, except that of long-wall. A number of 
mines, situated along the line of the Niles and New Lisbon Railroad 
were opened out on the long-wall system some years ago, with satis- 
factory results, but during the late panic, operations were suspended. 
On resuming work two or three years ago, the mining proprietors changed 
hands, and the new manager changed the plan to pillar and room 
practice. 
A large amount of coal has been lost, and some valuable coal is 
still being lost by faulty systems of mining. The first mines opened in 
the State were drift workings, opened in hills along the lines of outcrop 
of the coal. These hills, penetrated in all directions with ravines, gen- 
erally contained only a few acres of coal, and the overlying strata were 
not heavy. Very light pillars sufficed to support the roof under such 
circumstances, 
As the coal trade began to ee and the mines became more 
extensive, the frail supports, which sufficed for small mines, were found 
inadequate for those of larger extent. ‘The result was the falling in of 
the workings before they were fairly opened out. In reopening them 
larger pillars were left ; this, however, was done grudgingly, for the larger 
the pillars left, the greater is the expense of getting the coal. Coal 
lands were, however, abundant and cheap, and the cost of opening 
new mines was inconsiderable; hence, there was a temptation to adopt 
any system which would reduce the immediate cost of working toa 
minimum. 
When shaft mining became a necessity, and the first ton of coal 
cost the mining adventurers ten or twelve thousand dollars, better sys- 
tems were adopted from a sense of true economy, until by degrees, in 
all the mining districts of the State, improved systems were adopted ; 
though there are still mines in every district very unskillfully managed. 
In all our well-regulated mines the plans which generally obtain, 
