COAL MINING. 357 
districts, the pillars are removed as the workings advance. As soon as 
a range of rooms is worked out, the pillars are attacked and worked 
back to the entry. The advantage of this system consists in getting 
the pillar coal while it is yet fresh; for coal deteriorates by drying 
out, when left in the pillars for a number of years. ‘The expense 
of making new roadways is also avoided, but it requires skill, not always 
met in the management of mines in this State, to anticipate the results 
of drawing pillars, and quite frequently, the crush which follows their 
extraction, overruns the entries and destroys the whole economy of the 
mine. Experience, which is a good schoolmaster, is, however, throwing 
valuable light on this subject. 
A plan of mining which still largely obtains in this State, consists 
in driving single entries, and starting rooms from off both sides of the 
butt entries. Doors are placed in the mouths of rooms on one side of 
the entry, and the air is carried forward along the entry, and returned 
inside of the doors. Less expense attends this plan, especially in low 
mines, in which the roof requires to be blasted along the hauling roads, 
than by driving double entries, but the ventilation is never as good, and 
any saving effected is usually swallowed up by strikes and stoppages, 
occasioned indirectly at least by bad air. 
The above methods of mining, or some suitable modification of 
them, are practiced in every mining district of the State. Year after 
year improvements continue to be made, and many of our mines in 
their intricate subterranean departments show highly creditable en- 
gineering skill. 7 
A simple plan of working mines still lingers in the Hocking Valley, 
known as the block system. It seems to have been borrowed from the 
Monongahela River region in the early days of mining, and is applied 
only by mining superintendents who have never seen better practice. 
It consists~in dividing up the mine into a series of blocks or squares of 
- 800 or 400 feet, all the entries and air-courses being single. The objec- 
tion to the plan lies in the difficulty in getting forward air, and it is 
only practicable in mines which make no fire-damp and little of any 
other mineral gas. It has nothing to commend it, not even the plea of 
economy, and is disappearing before more advanced systems of working. 
In forming the blocks, the entrymen are required to work 500 to 600 
feet ahead of the air-ways. To do this, rooms are usually not allowed 
to be opened until the air-courses are completed ; sometimes, however, 
