164 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



"bings" at old disused collieries or shale mines, may be of 

 interest in this connection. 



Coal, oil-shale, and ironstone, particularly the last-named 

 mineral product of the Carboniferous formation, is associated 

 with black argillaceous shale, or " blaes " as it is called in 

 Scotland, which must be removed to make room for the miners 

 to work the valuable mineral. Ironstone seams, being, as a 

 rule, less than a foot thick, produce large blaes bings and are 

 thus expensive to work, since for every foot of useful ironstone 

 one or two feet of useless blaes must be excavated. 



Blackband and clayband ironstone are always associated with 

 blaes — the mud of the Carboniferous waters — but coal seams, 

 which are generally thick enough to be worked without removing 

 much extraneous material, are often associated with sandstone, 

 fireclay, or sandy blaes, and hence both the amount and quality 

 of the rubbish at the mouths of old pits depends on whether 

 coal or ironstone has been the mineral worked. 



The rubbish heaps again sometimes contain, or consist of 

 alum shale produced by the decomposition of iron pyrites or 

 marcasite (the sulphide of iron). This mineral, when oxidised, 

 produces sulphuric acid, which combines with part of the 

 alumina in the blaes to produce sulphate of alumina, or alum, 

 a soluble salt, absolutely destructive to vegetation. Wherever 

 shale of this kind occurs, the heaps remain bald and bare for 

 many years, and not even a blade of gra^s will grow on them. 

 Indeed, I know of one such heap on a hillside, where whenever 

 there is a wet season the water that runs off is so poisoned, that 

 a brown streak of dead grass may be seen extending down the 

 slope along the track of the noxious flood. Needless to say 

 such a soil would at once destroy the hardiest trees, and before 

 considering the afforestation of old bings, the absence of pyritous 

 shale should be made sure of. 



In the Lothians a third kind of mine refuse is produced in 

 vast quantities, and the production will continue to increase as 

 long as the oil-shale industry lasts. Oil-shale contains about 

 25 per cent, of volatile matter and carbon, and 75 per cent, of 

 ash. The latter is thrown out in enormous heaps, compared 

 to which the largest bings at coal or ironstone pits are but as 

 mole-hills to volcanoes. These "spent shale" bings generally 

 go on fire, in time, either spontaneously or because the materials 

 are emptied hot out of the retorts, where the organic matter has 



