64 ILLINOIS ACADEMY OF SCIENCE. 



miner, and the roof is taken down where necessary to maintain 

 roadways. Under this system all of the coal can be recovered, 

 but as a matter of fact shut-downs occasion some loss, because 

 of falling roof and irregular alignment of the mining face. Re- 

 mote corners of property may also be lost. However, recovery of 

 95 per cent is possible in spite of such losses. If the same method 

 were applicable to all Illinois mines our conservation problem 

 would be largely solved. 



Unfortunately, the strata above the thicker coals of the State 

 are so varied in character and strength that the room-and-pillar 

 method is commonly necessary. Narrow passages are cut in the 

 coal to serve for haulage and air circulation. Wider rooms are 

 then mined out with the aid of coal pillars and room props to 

 sustain the roof. It has been the common practice to abandon 

 pillars when the rooms are finished. 



One reason for leaving the pillars is that under prevailing 

 systems, which prescribe narrow pillars and wide rooms, it is 

 expensive, if not impossible, to recover the pillars. It may be 

 pointed out that, if the mines were worked on a panel system 

 with separate units surrounded by thick barrier pillars, and if 

 rooms were narrow and room pillars thick, practically all of the 

 coal could be recovered. It is encouraging to know that some 

 of the large companies are now installing this system. 



Another reason for leaving pillars is that surface subsidence 

 frequently causes damage suits. The actual loss from surface 

 subsidence should be negligible; for even with land values of 

 $125 per acre, and with total loss of 80 per cent, or $100, the 

 money loss would be only i per cent per ton of the coal in a 

 6-foot bed. As a matter of fact, the land would be as good as 

 ever after full settlement takes place and deranged surface 

 drains and tile systems are restored. 



An important loss in some parts of the State where thick coal 

 prevails comes from leaving i to 23^ feet of coal to form a roof. 

 It is needed to strengthen weak shale during advance work. 

 Although such coal can be recovered after rooms are worked out, 

 it is not uncommonly wasted. 



It is usually assumed that the room-and-pillar method yields 

 60 per cent of the coal, but it is probable than when unexpected 

 losses, due to carelessness, are included, the average recovery 

 for the State is not more than 50 per cent. A satisfactory remedy 

 has been advocated for the present losses with room-and-pillar 

 methods, but it is hard to introduce because it would increase the 



