. [Reports vol. I-XIII]. ere. When encountered in coal mining the coal is cut offabruptly, and, sometimes, the influx of water and sand is sostrong as to cause the abandonment of the mine. These chan-nels, therefore, not only reduce the area of the coal but furtherpresent obstacles to the operation of mining. 4. All coal beds have been deposited in basins of greater orless area and depth; they constituted, at the time of formationof the coal, great lagoons or swamps in which the material forLg„fig^,„ naturethe coal beds accumulated. The margins of such a swamp, or * o!i^ sea, consti
. [Reports vol. I-XIII]. ere. When encountered in coal mining the coal is cut offabruptly, and, sometimes, the influx of water and sand is sostrong as to cause the abandonment of the mine. These chan-nels, therefore, not only reduce the area of the coal but furtherpresent obstacles to the operation of mining. 4. All coal beds have been deposited in basins of greater orless area and depth; they constituted, at the time of formationof the coal, great lagoons or swamps in which the material forLg„fig^,„ naturethe coal beds accumulated. The margins of such a swamp, or * o!i^ sea, constituted the limits of each coal bed and towardsthese limits tlie coal gradually tapered to a feather edge. illustrates this idea and shows the manner in which such a 38 PRELIMINARY REPORT ON COAL. coal bed is subsequently covered by the succeeding deposits. In Taperingo£coal the Operations of mining, such a tapering coal bed is seldom, if ever, followed to its extreme limits, but work is generally Coal riG. 11. Diagram illastrating the lenticular nature oi Coal beds. abandoned long before this; as soou as the coal becomes reducedbelow a workable thickness. An extreme illustration of suchlimitation of a coal area is furnished by those remarkable depositsknown as coal pockets which occur in the rqgion Measures. Here the coal often attains a thickness of 20and more feet while the area of the basin may be only a fewacres. Such deposits have apparently accumulated in ravines orsink holes in the Lower Carboniferous and lower rocks, whichexisted before and during the Coal Measure period. THE CONDITIONS RESTRICTING AVAILABILITY. Thickness ofworkable beds, 1. Inadequate thickness is a condition restricting the availabilityof a coal which will be readily understood with little explana-tion, though just what thickness is inadequate is a relative and alocally variable term. Coal beds vary in thickness from an inch,or less, to many feet. In a region lik
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