108 Mr Bald on t?ie Fires that take place in Collieries. 



extent of the surface, and that the herbage in winter was of a 

 lively green. This induced the proprietor to convert part of this 

 grovmd into a nursery, for the rearing of forest trees ; and it 

 succeeded admirably, as the trees grew vigorously, and very 

 quickly ; but when they were removed from this genial clime, 

 produced by the subterraneous fire, to exposed situations, the 

 severity of the climate killed the plants, from the suddenness of 

 the change of temperature. 



This circumstance also shews how the internal heat of the 

 globe may diffuse itself in high latitudes, near the surface, and 

 produce in some degree the favourable effects of the climate of 

 the equatorial regions, in place of injuring vegetation, as we 

 would very naturally imagine. 



The Johnstone Colliery took fire by spontaneous ignition 

 above twenty years ago. It consists of five distinct beds of coal 

 lying close to each other, forming as it were one bed of coal, 

 constituting a thickness of above forty feet ; and in one place, 

 these five seams are overlapped, and constitute a thickness of 

 about eighty feet, which is an anomaly in the British coal for- 

 mation. It is also remarkable, that it is in a district abound- 

 ing with hard compact greenstone ; and the engine-pit, where the 

 drainage of the colliery is effected, commences in a bed of green- 

 stone at the surface, which is no less than 108 feet in thickness. 



When this coal-mine took fire, it instantly burst into flame, 

 and there being an open air-course betwixt two pits, it gained 

 strength, and burned with uncommon fury. Figure 7th, Plate 

 III. represents the situation of this mine with the two pits. 

 The fire commenced at the point a, betwixt the two pits ; the 

 atmospheric air descended the pit 6, and passing through the 

 burning mass, carried with it an immense volume of smoke, 

 which ascended the shaft c, and issued at its mouth, forming a 

 column of pitchy blackness, which rose to a great height 

 into the atmosphere, the air being calm. This had a terrific ap- 

 pearance: it continued in this state for some time, until this 

 dense vapour was heated to the igniting point, when it suddenly 

 burst into flame with a very loud explosion. This bright as- 

 piring flame, as thick as the volume of the pit, was at least se- 

 venty feet in height, and produced a very fearful but sublime 

 object. It instantly burnt down the machinery for drawing the 



