DATA were obtained by the writer from a number of the large coal-mine operators in Illinois, on the consumption and cost of timber used in their mines and the quality of the timber now being used as compared with former years.
The average cost for props in the longwall district has advanced from 0.75 cent per lineal foot in 1914, to 1.25 cents per lineal foot in 1921 , and a 7-foot timber costing 16 cents in 1914 now costs 25 cents. The maximum cost given in 1914 is 8 cents per ton of coal mined, whereas cost at one of the largest mines is now about 15 cents per ton mined.
The timber used in the room-and-pillar mines of Illinois is practically all mixed hardwoods. Both round and split props are commonly used, although some operators prefer the round props, as these are said to give better service than the split props. Probably more than 65 per cent. of the prop timber is mixed oak (red oak, white oak, burr oak, and other species of oak), the rest being sycamore, hickory, elm, and other varieties.
Cross-bars are principally white oak, with some red oak, burr oak, and a little walnut. The diameter at the small end ranges from 4 to 8 inches, 6 inches being perhaps the most commonly used, and lengths from 8 to 20 feet, depending on the width of the opening to be supported. The majority of the operators use only white oak for mine ties, although many accept any kind of hardwood.
A large part of the mine timber used in Illinois mines is shipped in, chiefly from Missouri. In some of the mining districts the local supply of timber obtainable for mine use is limited in quantity and of inferior quality. The cost at the mine varies, according to the length of haul and minimum diameter that the operator will accept, from 16 cents for a locally grown 7-foot prop with 2~-inch tip, to 28 cents for a Missouri white oak prop of the same length and measuring 5 inches diameter at the tip.
* Communicated by H. Foster Bain, Director.