MINE TIMBERING IN THE UNITED STATES. … LIGHT TIMBERS USED IN CAVING SYSTEMS. and the table below is presented merely ly for mine supports one million or to indicate the extent of the mining in- more feet, board measure, of timber. dustry of the United States. Accord- It will, therefore, be evident that the ing to the reports of the…
Engineering
Internet Archive · Smithsonian Libraries · Public domain (published before 1931). Free to use for anything.
