96 STEVENSON— FORMATION OF COAL BEDS. [April i8. 



always a terrible obstacle for exploring parties. Equally in the 

 White Mountains of New England and in many portions of the 

 Appalachians, the writer has seen forests of bare stems projecting 

 above the young growth in areas which had been devastated by fires. 

 The coals of Iowa and Missouri, in some beds, contain so much 

 mineral charcoal that one would have to imagine a continuous con- 

 flagration for the whole area during accumulation of the coal. 



Variations in Chemical Composition. 



The independent history of the several benches of a coal bed is 

 shown not only by the physical contrasts but also by the contrasts in 

 chemical composition, which often are very great. Study of these' 

 makes evident that the period of time represented in some localities 

 by a half-inch parting of mineral charcoal and impalpable clay may 

 have been so long as to bring about serious changes in the surround- 

 ing conditions. Here one is concerned only with contrasts which 

 seem to be original and not with those which may be due to influence 

 of agencies belonging to later times. 



The Bernice coal basin in Sullivan county of Pennsylvania is 

 almost 40 miles from the anthracite area and the dips are extremely 

 gentle. The area is insignificant, 600 yards wide and 2,400 yards 

 long; yet it affords illustrations of differing composition which show 

 the influence of very local conditions. The basin was described by 

 Piatt and the analyses were made by McCreath.^*^- Piatt's section 

 shows two coal beds separated by 65 feet. The lower, 2 feet thick, 

 has 



Water 4.130 



Volatile matter 15-270 



Fixed carbon 67.362 



Sulphur 0.523 



Ash 12.715 



with a fuel ratio of i 14.41. Another analysis from a different part 

 of the mine has very slightly less volatile but 3 per cent, more of 



"=A. S. McCreath, Sec. Geol. Surv. Penn., Rep. MM, 1879, PP- 82, 94, 97; 

 F. Piatt, ibid., Rep. GG, pp. 176, 189-193. 



