17
STATISTICS OF COAL PRODUCTION.
position, and distribution of pillars aside from the one-third rule. Consequently, the pillars are not columnized; in other words, they are not exactly over each other. Many of the thick beds of the middle measures under the Hyde Park and Providence sections are close together. Therefore the pillars in these thick beds, not being columnized, have a decided tendency to crush through the interval between the beds, the pillars of an upper bed settling into the excavations or rooms of the lower workings.
Another feature that should be brought out in this historical sketch of early mining in Scranton is that the universal practice in the old days was to mine only the best, thickest, and most accessible coal beds, and also only the profitable parts of each bed, and to leave unmined, as refuse, the parts which for one cause or another were found more expensive to work. Therefore, in these latter days some of the coal beds already mined over and ready to be abandoned have been found to carry rider coal above or bottom coal below, which can be removed at a profit. And, therefore, for the past few years the total production from several beds has been from such remining of top and bottom coal. This remining, of course, leaves the pillars from 2 to 6 feet taller than they were before for the same horizontal area, consequently the pillars are much weaker and less able to support the overburden.
In consequence of the several conditions related above there have been from time to time numerous and more or less serious caves or subsidences of the surface, principally on the west side, which have caused some damage to surface property, but no loss of life. In every instance the damage has been speedily repaired and temporarily forgotten. The accumulated result of these repeated subsidences has probably left certain parts of the surface in that section of the city in more stable condition than they were before. This phase of the subject, however, will be considered in a subsequent chapter.
STATISTICS OF COAL PRODUCTION.
The following statistics of the coal-mining industry in Scranton are based upon the result of the surface and underground investigations made by us, and from our inspection of the mine maps, taken in conjunction with the annual production of coal as shown in the published statistics contained hi the reports of the State mine inspectors.