200 STEVENSON— INTERRELATIONS OF THE FOSSIL FUELS. 



invaded it, and the stems, still erect, extend into the coal ; but at 

 Orebkau, the condition appears to have been different. There, logs 

 increase downward until at the bottom they constitute practically the 

 whole mass. The forest growing in loose material must have been 

 overthrown, for in the mines examined by Russwurm, no erect stems 

 were seen. Many beds of brown coal seem to be wholly without tree 

 trunks, just as there are many peat bogs without fragments larger 

 than a twig; these had not reached the stage of tree-growth. Inter- 

 ruptions in growth are equally characteristic of peat bogs and brown 

 coal beds. Some are shown by partings containing much mineral 

 charcoal, others by partings of transported mineral matter, while 

 others still by the forest layers. At Bovey Tracey, a great mass of 

 leaves in the lower part of a thick bench is the remaining evidence of 

 a dicotyledonous forest, whose non-resinous stems have disappeared. 

 A succession of forests is shown at Senftenberg, even to the last, 

 which was entombed in the covering sands as was that at Wurzen in 

 Sachsen. The great forest bed of the Hardt area marks a long, 

 though not total interruption; growth of normal peat ceased for the 

 time, but accumulation most probably continued ; offal from conifer- 

 ous trees accumulates to notable thickness in many parts of the world 

 without injury to the trees; Capps has shown that in Alaska, where 

 the plane of perpetual frost is at only a few inches below the surface, 

 the gigantic spruces adjust themselves to the conditions and throw 

 out new sets of roots as the peat surface rises. 



The benches of a coal bed often are dissimilar. One finds no 

 evidence of widespread climatic changes during the period of a 

 single bed's growth. In most cases, there is evidence of notable 

 variation in moisture conditions and dryness appears in some locali- 

 ties to have prevailed for long periods ; but there is no evidence 

 that these variations were due to any but local causes. They are 

 much like those which may be seen in almost every peat deposit. 

 At Bovey Tracey, one bench is composed almost wholly of fronds 

 of ferns while another is a mass of Sequoia stems ; near Budweis, the 

 upper bench contains stems completely coaled, while the lower bench 

 is composed mostly of the imperfectly changed Moorkohle. Hantken 

 has described a bed of which the upper part is woody, crowded with 



