324 COALFIELDS AND COLLIERIES OF AUSTRALIA. 



perature is about 330 degrees C. Coal naturally absorbs oxy- 

 gen from the air, and undergoes a process of slow combustion. 

 Marcasite, when decomposing, swells, breaks up the coal, and 

 thus exposes a large surface to oxidation. A gob fire starts 

 gradually; first there is an increase in temperature, followed 

 by an unmistakable smell of gob stink owing to the volatile 

 matter being distilled off, and a mist is formed. 



The downcast shaft is 15ft. in diameter and 420ft. deep, 

 and about half a mile distant is the upcast, which is rectangu- 

 lar in section, 10ft. by 5Jft., and 201ft. deep. There is also a 

 tunnel entrance 36 chains from the downcast shaft, which was 

 used as a travelling way for men and horses. 



The coal was extracted on the bord and pillar system. The 

 bords averaged 24ft. wide, while the pillars varied from 12ft. 

 to 45ft. Cut-throughs connected the bords every 105ft. The 

 first working was carried forward in the lower or 9ft. section 

 of the top seam, until the cut-through was connected, when 

 they worked the top section back in the reverse direction. The 

 "brassy tops" were left standing, but they eventually fall, 

 sooner or later, for want of support. Fire damp had been occa- 

 sionally found in very small quantities, but it had been detected 

 rising from the heated debris. 



There have been eight fires in this mine altogether ; seven, 

 due to spontaneous combustion, and one to a naked light. For 

 information concerning these fires I am largely indebted to 

 Mr. J. Jeffries, who was formerly in charge of this colliery,, 

 and has given an account of it in his paper entitled "The 

 Occurrence of Underground Fires at the Greta Colliery, New 

 South Wales." (Trans. Inst. Min. Eng., 1904-05, XXIX, p. 

 518). The first fire occurred in 1897, at a point where water 

 dripped from the roof on the fallen "brassy tops/' which ac- 

 celerated chemical action. Having been observed while in the 

 incipient stage, it was easily filled out. A. few months after 

 the second fire, a creep occurred, resulting in the loss of a 

 district. Large volumes of water held in the strata were li- 

 berated, and as the pumping machinery was not sufficient to 

 keep the water down, it was turned into the dip working. 

 The creep cut off the ventilation from the greater portion of 

 the affected area, and as was also the case with subsequent 

 fires, direct attack was too slow to be effective, so it was at- 

 tempted to isolate the area by building stoppings. These 

 were built of brick, or brick and clay, also of timber and loamy 

 sand, when the crushed condition of the pillars made a tight 

 joint with brickwork impossible. 



Mr. Jeffries writes that, "The experience gained in deal- 

 ing with these underground fires emphasises the difficulty of 

 coping with such evils by the sealing off process, and also the 



