Manawatu Daily Times [ESTABLISHED 21st MAY, 1876.} WEDNESDAY, DECEMBER 21, 1921 AMERICAN COAL MINING.

Manawatu Times, Volume XLVI, Issue 2004, 21 December 1921, Page 4

Manawatu Daily Times [ESTABLISHED 21st MAY, 1876.} WEDNESDAY, DECEMBER 21, 1921 AMERICAN COAL MINING.

Direct comparison between methods ; and results of coalmining in America and Britain is not possible because the conditions vary greatly. Most of the thick seams in Britain are practically exhausted, while those in the United States are so numerous that only the best and thickest need be worked. Even in these, about half of the coal is left in place to support the roof, so that little timbering is required, whereas in most British mines the extraction amounts to about 90 per cent., and the cost of timbering-, in several instances, is over 3/ per ton of coal raised. Very few mines in America exceed a depth of 500 ft., while some of the British mines are 3000 ft. deep. Tliis obviously increases the cost of winning the coal and the difficulty of pumping and ventilating the mine; the higher temperatures encountered in deeper mines also tend to reduce output. In addition to these natural advantages, machinery is used to a much larger extent in American than in British mines. Many coalfields are worked by the open-cut method and are simply quarries, the covering material being removed by large excavating machines and the exposed coal dug and loaded by smaller machines of the same class. Where coal mined underground, large undercutting, ripping and shearing machines are employed, some of which undercut the coal to a depth of 12ft. In some cases fliachines are used to break down the coal with mechanical picks, collect and deliver it directly into tubs. With such machines operated by two men an average output of 21 tons an hour can be obtained for a whole week's working.