STEVENSON— INTERRELATIONS OF THE FOSSIL FUELS. 145 



noted here that " bitumenization " as used by Horner and others of 

 the earher writers is practically synonymous with " coalification " 

 of some French writers and refers merely to the extent of conversion. 



The several kinds of coal are found at times in a single bed. The 

 wood is ordinarily in fragments of inconsiderable size, but some- 

 times large stems are found. These, when prostrate, the usual posi- 

 tion, are flattened; but trees have been met with, erect, with roots 

 attached and the stems passing through some benches of the coal. 

 Horner thinks that these may have been floated in, being held in posi- 

 tion by the weight of the roots. One of these trees w^as 7 and 

 another 1 1 feet in diameter ; the depth of water in which such trees 

 could be floated must have been considerable. The writer has seen 

 great floods on great rivers and he has seen many floating trees with 

 roots attached, but he has never seen one floating in vertical posi- 

 tion, except w'here it seemed wholly probable that the roots were 

 loaded with earth or stones. If these trees near Bonn had been 

 floated in erect position, the inorganic materials ought to appear with 

 them. Horner states that the wood is often well enough preserved 

 to be utilized in timbering the mines. Pyrite is common and " amber" 

 occurs in irregular balls. The wood, at times, is replaced in part or 

 altogether with carbonate of iron. 



The section of a shaft at Utweiler is as follows: Soil, 2 feet 6 

 inches; loess, 9 feet 5 inches; basalt, 31 feet 9 inches; indurated clay, 

 prismatic, changed by the basalt, i foot ; clay, coaly, neither slaty nor 

 columnar, 6 inches ; black pitch coal, in prisms, perpendicular to face 

 of the basalt and with dolomite in the interstices, i foot 2 inches; 

 small coal, 4 feet ; brown coal or bituminous wood, unaltered and 

 with structure preserved, contains in the lower portion kidneys of 

 compact clay-ironstone, 8 feet 6 inches. 



The influence of the basalt disappears within 7 feet. The con- 

 stitution of the thick bottom coal recalls the condition so often seen 

 in the lower part of peat deposits formed by encroachment upon 

 forested areas. 



Heusler-°^ has given a full description of conditions in the Lower 



204 C. Heusler, " Beschreibung des Bergreviers Brulil-Unkel und des 

 Niederrheinischen Braunkohlenbeckens," Bonn, 1897, pp. 32-42, 45-52, 132, 

 161, 163. 



