STEVENSON— INTERRELATIONS OF THE FOSSIL FUELS. 201 



Sequoia, while the lower part is hard coal. At Orebkau, the upper 

 bench is Knorpelkohle, with very little wood, while the lower bench 

 is Formkohle with much wood. Variations of similar type are re- 

 ported from American localities and they are such as are familiar to 

 students of peat deposits. They are so characteristic that one finds 

 it difficult to avoid the conclusion that, as in peat bogs, the process of 

 conversion was arrested in some benches while it continued in others. 

 It seems hardly possible that the dififerences developed after burial, 

 as conditions since that time must have been practically the same for 

 all portions of the deposit. 



The differences in physical features are accompanied by differ- 

 ences in chemical composition. The lower portion of the coal bed 

 on Advent Bay, Spitzbergen, has 9 per cent, more volatile than is 

 found in the upper portion. Coals from different parts of the same 

 mine show even greater contrast; 18 per cent, near Gran in Hungary, 

 23 near Brennberg in the same kingdom, 35 at Glendive in Montana ; 

 and similar variations are shown by analyses of samples from neigh- 

 boring mines on the same bed. The ash content tells the same story ; 

 in six mines on the same bed, near Rockdale, Texas, the ash varies 

 from 9.43 to 24.67. The comparison is more instructive when one 

 considers the composition of the ash, for the samples analyzed were 

 prisms representing the full thickness of the seam, only such part- 

 ings being removed as should be separated before shipment of the 

 coal. The silica is from 21 to 47 per cent., alumina from 12 to 28, 

 ferrous oxide from 2 to almost 25, lime 6 to 38 and sulphuric acid 

 4.58 to 18.01. These samples were taken in an area of probably not 

 more than 2 or 3 square miles. It would appear that conditions 

 during accumulation varied greatly in the different parts of even 

 small areas, just as they do in the swamp areas of this day. 



Sapropelic or Lebertorf material is an important constituent of 

 many swamps, though there are very many in wdiich no trace of it 

 exists. It has been reported occasionally from the Tertiary coal. 

 Dall obtained at Amalik Harbor, Alaska, a dull coal which contains 

 81.26 per cent, of volatile matter; at Mendota in Washington there 

 are lenses of what appears to be Lebertorf, the coal having all the 

 features of cannel and burning with a long smoky flame; lenses of 



