Editorial Comment. 47 
mining. "The large shipments of our railroad companies seem 
to be for tiie purpose of secui-ing the most tonnage possible, and 
lead to the working of mines for large production more than 
careful mining. Those who own lands are exercising more 
care in mining, so as to seecure a continuance of the supply. 
But when we have large coal beds, say from 20 to 40 feet in 
thickness, as in the Mahanoy district and part of the Wyoming 
region, how can we secure half of the coal if we must support 
the surface? Neither timber nor even iron props will answer 
the purpose. Any bed of coal less than ten feet in thickness 
can be mined so as to secure three-fourths of the coal. In bitu- 
minous beds you can rob the pillars and let the surface fall and 
no harm results. The same is true in smaller anthracite beds. 
But when you have to mine the Mammoth bed, you cannot 
confine the great pressure of the surface to a small area. The 
heavy sandstone rock which covers it, when disturbed by the 
removal of a pillar, brings on a pressure that affects the whole 
mine. * * * * There has been recently adopted a plan 
at the workings of the Kohinoor colliery, in the Shenandoah 
district in Schuylkill county, that, I think, will enable us to 
secure three-fourths of the coal in the mine. At this point the 
Mammoth bed is 40 feet thick and lies nearly horizontal. To 
support the surface and the town upon it, will naturally re- 
quire grejt pillars of coal, at least half of the mine. The plan 
devised, and now being worked, is to bore through the superin- 
cumbent strata, 400 feet thick, eight-inch holes to the top of 
the coal bed. Cast-iron troughs 10x12 inches wide, with con- 
tinuous bands of scrapers moving in tiiem, or what is now call- 
ed a "scraper line," connect with the immense culm banks at 
the breaker, some 1,600 feet distant. The scraper line delivers 
continuously a large amount of culm at the mouth of the hole. 
This meets there a stream of water, and a mixture of about 
three-fourths water and one-fourth culm constantly drops into 
the river below and there distributes itself, permeating every 
nook and corner of the cavities. The deposit becomes so hard 
as to require a pick to remove it. It entirely fills the chamber 
even to the roof, and supports the pillars, but leaving them 
accessible to the miner for removal when the large spaces sur- 
rounding them are entirely filled. Of course we must direct the 
currents of water and culm, limiting the culm by dams or 
