GRETA COLLIERY. 323 



Cashes. Tlie gob stink, the smell of a newly lighted coal fire, 

 once experienced never to be forgotten, is noticeable in the 

 neighbourhood of these heaps. 



This colliery was worked for 20 years. There are two 

 seams, 14ft. apart, but only the No. 1 or top seam was worked. 

 This was extracted in two sections, and was made up as fol- 

 lows : 



Coal, brassy tops 1ft. 3in. 



Band . Oft. lin. 



Coal 1ft. Oin. 



Band Oft. lin. 



Coal . . . 3ft. Oin. 5ft. 5in. second working. 



Indurated clay band 

 thickly studded 

 with plant im- 

 pressions locally 

 termed " white 



stone" Oft. 6in. 



oal 4ft. Oin. 



Blackstone band . . Oft. Gin. 



Coal 4ft. Oin. 9ft. Oin. first working. 



14ft. 5in. 



The top seam varies considerably in thickness, but may 

 l)e taken to average 14ft. 6in., the bottom seam being 3ft. Tin. 

 thick. The roof consists of a band of coarse conglomerate im- 

 mediately above the "brassy tops" for a few inches in thick- 

 ness, followed by extremely soft sandstone, which decomposes 

 into firm sand on exposure to the atmosphere. Mr. Jeffries, 

 the late mine manager, thinks this has much to do with the 

 gob fires, for, falling as it does, immediately after the "brassy 

 tops," it acts as a covering or blanket, and being a bad con- 

 ductor of heat, when chemical action occurs, the heat cannot 

 rise to the surface to be cooled by the ventilating current, 

 so the temperature gradually increases till the ignition point 

 is reached. "Brassy tops" are shales containing marcasite, 

 the latter decomposing into sulphate of iron, which weathers 

 white. "Brasses" also occur in the coal in places, more es- 

 pecially w T hen the coal is broken up. It does not occur in 

 nodules, but is generally found in streaks predominating along 

 certain bedding planes. It is not continuous, showing prefer- 

 ence for the brittle black bituminous portion of coal. It also 

 occurs in vertical joints of the coal, so was evidently precipi- 

 tated after the coal was formed, not simultaneously with it. 

 Tinely pulverised bituminous coals in contact with air begin 

 io oxidise between 120 and 155 degrees C. The ignition tern- 



