19I3-] 



STEVENSON— FORMATION OF COAL BEDS. 



105 



Silica 



Alumina 



Oxide of iron... 



Lime 



Magnesia 



Sulphuric acid.. 

 Phosphoric acid 



Titanic acid 



Alkalies, loss... 



Red Ash. 



47.190 

 35-522 

 4.700 

 3.640 

 0.965 

 0.712 

 1.958 

 0.990 

 7-313 



White Ash. 



48.250 



36.177 

 3.290 

 1.950 

 0.921 

 0.490 

 0.923 

 0.750 

 7.249 



Clinton. 



47-585 

 40.117 

 6.143 

 0.960 

 0.731 

 0.392 

 0.123 

 1. 190 

 1.486 



5.590 to 74.800; lime from 1.080 to 21.540; magnesia from o to 

 9.823 ; potash and soda from o to barely i per cent. McCreath 

 reports a small quantity of alkalies in nearly all cases. Where the 

 proportion of iron is large the coal is pyritous. Potash is present in 

 all terrestrial plants, though not always as carbonate. Dieulafait^^^ 

 examined the ashes of 168 specimens of recent Equiseta collected 

 at various localities in Europe and northern Africa. Alkaline 

 carbonates were wanting but calcium sulphate and potassium 

 sulphate are present in large proportion; yet plants of other types, 

 growing in the same localities, gave ash of the ordinary kind, rich 

 in carbonates and poor in sulphates. 



The ash analyses to which reference has been made are for the 

 most part from coals without notable commingling with slates. It 

 is altogether probable that ash from commercial samples would show 

 the same materials, though no doubt in shghtly different proportions, 

 as it would contain silts brought in and deposited on the forming 

 coal. But in this connection, one must not forget that wind may 

 contribute towards addition of foreign materials. The presence of 

 atmospheric dust is an only too familiar phenomenon on sea as well 

 as on land, but one is in danger of underestimating its importance. 

 James Douglas has informed the writer that coke from Connells- 

 ville, exposed in heaps to the winds of Arizona for a few weeks, 

 showed almost 30 per cent, of ash, though it originally contained 

 not more than 14. This change was in the arid region where dust 

 is abundant, but it suffices to show the possibilities elsewhere. 



^" M. Dieulafait, " Composition cles cendres des Equisetacees," C. R., Vol. 

 100, 1885, pp. 284-286. 



