CHAPTER XV 

 MINE TIMBERS 



GENERAL 



In the early history of this country comparatively little mining 

 beneath the ground was carried on. However, with the development of 

 coal mining, principally in Pennsylvania, a heavy demand was gradually 

 created for mine timbers in both the sawed and round forms. At first 

 the only means of support were " mineral pillars," which consisted of 

 pillars of ore left in the chambers as a means of support. As the value 

 of the minerals increased and the operations became enlarged and more 

 systematized, wooden supports called props, caps and collars were 

 substituted for the old mineral pillars. 



Wood has given great satisfaction and although it is possible that 

 concrete and steel may, to a limited extent, replace the wooden supports 

 in the various types of mines, their comparatively high cost and the dif- 

 ficulty of installation will doubtless restrict their use to a considerable 

 degree. 



It is estimated by the U. S. Geological Survey that there are approx- 

 imately 50,000 mines in this country. However, probably only 5000 of 

 these use timber for props, caps, collars, lagging, mine ties, shaft shoring, 

 etc. There are many mining operations classified as mines according 

 to the government statistics, but a large number consist of quarries, 

 placer mines, oil and gas wells, salt works, clay pits and coal strippings, 

 which use little wood. 



The only available complete figures showing the use of timber in 

 mines were compiled by R. S. Kellogg in 1905 for the U. S. Forest Service. 

 This compilation estimated that we use in round numbers about 200,000,- 

 000 cu. ft. or about 2,500,000,000 bd.-ft. of round and sawed timbers. 

 At the present time (1919) this material would be valued at about $13,- 

 000,000. Of the total amount only about 17 per cent is composed of 

 sawed timbers and lumber. 



Most of the mines gather the round timber material from the region 

 about the mines, 



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