suggestions of bischof and lesley. 63 



Bischof's Theory of the Formation of Anthracite. 



Long ago Bischof recognized that graphite is of vegetable origin, the 

 mode of its occurrence in coal-beds of Greenland as well as in those near 

 Cumnoch, in Scotland, being such as to leave no room for doubt. As 

 anthracite is intermediate between bituminous coal and graphite, its 

 vegetable origin was conceded of necessity. Lesley* has shown b}'' tabu- 

 lating the anah'ses made by A. S. McCreath that the series from the 

 driest anthracite to the richest bituminous coal is almost perfect. 



Vegetable matter left exposed upon the ground decays ; it is oxidized 

 and loses its own oxygen very rapidly. This process does not convert 

 wood into coal, the escaping gases being carbon-dioxide and water ; but 

 under water the change advances different! 3^, so that the carbon and 

 hydrogen unite, and marsh gas as well as the other gases mentioned is 

 set free. Goejipert f found that the decomposition of mosses goes on more 

 slowly as the depth of the water increases ; those at 6 to 8 inches below 

 the surface decompose rapidly, but others at 12 to 36 inches were fairly 

 preserved for fifteen months. The character of the decomposition may 

 well assume different characters with var3^ing deptlis of water. Bischof f 

 thinks that the smaller quantity of volatile h\^drocarbons in anthracite 

 fields may be due to the more ready access of water, which favored evo- 

 lution of marsh gas as well as the other gases. Sterry Hunt § has ex- 

 hibited the several steps in the j^rocess of change from cellulose to bitu- 

 minous coal by a series of empirical formulas, which show the successive 

 conditions mentioned by Bischof. Green || has illustrated the relations 

 of the several products from wood to anthracite by a table of percentage 

 compositions. 



Lesley's Suggestion of Oxidation. 



Professor Lesley uses the process of oxidation as the basis of a sugges- 

 tion respecting the possible origin of the Pennsylvania anthracite. He 

 lays great stress upon the fact that in the anthracite region there are more 

 of sandy and gravelly rocks than in the bituminous regions, where clayey 

 materials abound, so that oxidation of the coal would be favored in the 

 former more than in the latter. He maintains, further, that the undis- 

 turbed clays of the latter lute down and almost hermetically seal the 

 underground coals, whereas the disturbed, semi-metamorphosed and 

 cracked-up clay-slates of the former expose their coals to the very bottom 

 of the series to percolation, evaporation and oxidation. 



* Lesley in Second Report of Progress in the Laboratory, etc, 1879, p. 146 et seq. 



tGoeppert cited by Bischof, Chemical Geology, vol. i, p. 271. 



X Bischof: Chemical Geolog.v, vol. i, p. 273, foot-note. 



g sterry Hunt : Chemical and Geological Essays, 1875, p. 181. 



B Green : Geology, 1882, part 1, Physical Geology, p. 182. 



IX— Bull. Geol. Soc. Am., Vol. 5, 1S93. 



