MINE TIMBERS 335 



the warm moist air in most of the mines, the timber is readily subject 

 to attack by decay and insects. In coal mines it very frequently happens 

 in extreme cases that the timbers up to from 12 to 15 in. in diameter will 

 become completely decayed in about three years if used in the untreated 

 condition. The expense involved in resetting these timbers is very great, 

 and furthermore, such replacements generally interfere with the working 

 operations of the mines. 



Besides decay, other prominent reasons for the destruction of mine 

 tmbers are wear and tear, breakage, fire and wastage. Taken all 

 together, these represent about 50 per cent of the causes for the destruc- 

 tion of mine timbers, the remaining 50 per cent being the result of decay 

 and insect attack. Wooden rollers and drums must be frequently 

 replaced on account of wear, and large amounts of timbers themselves 

 destroyed by " crush " and " squeeze," or by " swelling ground " and a 

 great deal of temporary timber is lost in mine workings which become 

 filled with waste rock and dirt called " slush " after the coal and other 

 ore has been mined. 



The relative importance of the various destructive agencies in the 

 American mines is shown in the following table i^ 



Causes of Destruction. Percentage. 



Decay and insect attack 50 



Waste from all causes 25 



Breakage and fire 20 



Wear 5 



BIBLIOGRAPHY 



Bureau of Census. Forest Products of the United States, 1907. Washington, 

 D. C. 



Kellog, R. S. Timbers Used in the Mines of the United States in 1005. Forest 

 Service Circ. No. 49. 



Rocky Mountain Mine Timbers. Forest Service Bull. No. 77. 



Mason, D. T. Utilization and Management of Lodgepole Pine in the Rocky Moun- 

 tains. . Forest Service Bull. No. 234. 



Nelson, John M. Prolonging the Life of Mine Timbers. U. S. Forest Service 

 Circ. III. 



Peters, E. W. Preservation of Mine Timbers. Forest Service BuU. No. 107. 



Weiss, H. F. Preservation of Structural Timber. 



1 From " The Preservation of Mine Timbers," by E. W. Peters, U. S. Forest Service 

 Bull. 107, 1912, p. 6. 



