EOCKY MOUNTAIN MINE TIMBEES. 11 



dead material tested was cut from an area supposedly burned over 

 in 1880. In general, the surface was covered with a network of 

 shallow worm marks (made when the bark was on and probably of 

 no influence on the soundness). The beams, even the larger ones, 

 were very rough and knotty, and were of poorer grade in respect to 

 condition of knots than those cut green. The cross sections in gen- 

 eral were sound, though here and there along the length were places 

 beginning to form punky pockets at the surface. The fact that this 

 material under test gave values up to the elastic limit nearly equal 

 to those of the air-dried beams is of considerable interest, as it indi- 

 cates that it is in excellent condition for the uses to which round 

 material is ordinarily put. 



CONCLUSIONS. 



The tests indicate that : 



1. An air-dried mine prop is superior to a green one as follows: 



Strength at elastic limit 2.3 times as great. 

 Strength at maximum load 2.3 times as great. 

 Stiffness 1.9 times as great. 

 An air-dried mine cap is superior to a green one as follows: 

 Strength at elastic limit 2.2 times as great. 

 Strength at maximum load 1.6 times as great. 

 Stiffness 1.4 times as great. 



2. With the exception of Douglas fir, there seems to be as much variation in the 



strength of one species procured in different places as among the different 

 species themselves. This is probably the result of defects such as checks, 

 knots, and bends, which, in this size of material (5 to 6 inch diameter round 

 caps and props), apparently overbalance the differences in the actual strength 

 of the clear wood. 



3. The unit strength and stiffness of 16-foot round beams decrease with an increase 



in size. The smaller beams tested, however, represented a slower growth 

 material and were probably suppressed trees. 



4. Beams cut from timber standing dead for about 30 years showed a strength in- 



termediate between green and air-dried material cut from live timber. The 

 tests tend to corroborate the opinion that timber cut from dead trees can be 

 graded on the same basis as other material; that is, the quality of the wood has 

 not changed, from the fact that it has seasoned on the stump, and deterioration, 

 if present, will be indicated by signs of decay. Checking in material to be 

 used in the round form can hardly be considered as a defect, as it occurs in all 

 air-dried round material. 



CONSUMPTION AND DURABILITY. 

 CONSUMPTION OF MINE TIMBERS IN COLORADO. 



The statistics here presented were collected to show the consump- 

 tion of timber by the mining industry of Colorado x in 1911. They 

 were obtained by sending a card to the mine operators of the State, 

 requesting them to furnish the amounts, costs, and species of tim- 



i Colorado was chosen partly because of its importance as a mining State; partly because for the year 

 1911 an estimate of the entire production of wood products, including lumber, poles, crossties, round mine 

 timbers, and fuel was also available for direct comparison, and partly because the State is near the center 

 of distribution of the species of mine timbers tested. 



