ABSTRACT
The difficulty and cost of winning and working coal-mines form an aspect of the question that obviously contains the solution of the whole. The question is a twofold one: is it physically possible to drive our coal-mines to the depth of 4,000, 5,000, or 6,000 feet? and, is it commercially possible when in other parts of the world coal is yet being worked in the light of day? The temperature of the air may be reduced by plentiful ventilation, or by letting out in the mine air compressed and cooled at the surface, as is done in the new coal-cutting machines. Much increased ventilation will be a matter of expense and difficulty; the hardening of the coal and rocks will render hewing more costly; creeps and subsidences of the strata will be unavoidable. The coal-measures themselves, containing many beds of clay and shale, are dry enough in general, except where interrupted by faults which allow the water to penetrate.
