76 STEVENSON— FORMATION OF COAL BEDS. [April 18, 



The Coaks bed contains great numbers of coal balls or plant- 

 sphaerosiderites ; Stnr obtained several hundreds in a large block of 

 coal shipped to him from the mine. These are especially abundant 

 in the upper bench and on the west side of the area, where the roof 

 balls also are most numerous. The remains of plants in the coal 

 balls are always well-preserved but those in the roof balls are in bad 

 condition. 



The roof balls, according to Stopes and Watson, have from 4 to 

 6 per cent, of clay, whereas the coal balls have often no more than a 

 trace. Stur has given two analyses of those from the roof, which 

 are quite dissimilar : 



Carbonate of calcium 61.43 29.01 



Carbonate of magnesium 2.86 4.33 



Carbonate of iron 16.13 25.09 



Carbonate of manganese 1.73 



Sulphide of iron 6.45 



Clay 2.49 2.22 



Insoluble matter 1303 30.20 



Water and loss 2.^,^, 2.70 



The coal balls show extreme variations in some constituents. 

 According to Stopes and Watson, those from Bacup are chiefly dolo- 

 mite; whereas several of those from Shore show very little magnesia, 

 and only 2 of the 5 specimens analyzed have more than 5 per cent, 

 of carbonate of magnesia. Stocks analyzed two from Yorkshire 

 localities, which gave 



Carbonate of calcium 64 82 



Carbonate of magnesium 2 0.75 



Sulphide of iron 21 12 



with small per cent, of sulphate of calcium, silica, clay and organic 

 matter. Sometimes the nodules contain pieces of fossilized wood 

 which are large enough for study. They also show much variation, 

 4 specimens giving 



Carbonate of calcium 86 24 87 49 



Carbonate of magnesium 4 2 3 6 



Sulphate of calcium 14 i 9 



Sulphide of iron 49 5 24 



