The points of observation and measurement are so closely spaced and the thickness and extent of coals are so well defined that the tonnage is judged to be accurate within 20 percent of true tonnage. Although the spacing of the points of observation necessary to demonstrate continuity of the coal differs from region to region according to the character of the coal beds, the points of observation are no greater than mile apart. Measured coal is projected to extend as a -mile wide belt from the outcrop or points of observation or measurement. The bearing is used to designate direction. The bearing of a line is the acute horizontal angle between the meridian and the line.
Azimuths are angles measured clockwise from any meridian.
Methane, which is the principal component of natural gas, is frequently encountered in underground coal mining operations and is kept within safe limits through the use of extensive mine ventilation systems. An electronic instrument often mounted on a piece of mining equipment, that detects and measures the methane content of mine air. The term employed to designate the operations involved in preparing a mine for ore extraction. These operations include tunneling, sinking, cross-cutting, drifting, and raising. A coal burning electric-generating plant built near a coal mine.