OBJECTIONS TO LESLEY's SUGGESTION. 65 



pile of rocks had been deposited, and that the process continued until 

 sometime posterior to the folding and crushing ; hut it is not easy to 

 understand how percolation would be carried on to Sinj greater extent 

 in the anthracite than in the bituminous region after the folding and 

 consequent erosion had taken place. Those who mine bituminous coal 

 find the water of percolation through the coal itself sufficiently trouble- 

 some in western Pennsylvania. Water of this kind would be stagnant 

 in the canoe synclinals, and as its oxygen would soon be converted into 

 carbon dioxide, the process of oxidation would be stopped. Bituminous 

 coal, it is true, when exposed to atmospheric moisture and a slightly 

 increased temperature, does undergo changes in composition somewhat 

 analogous to those which lead to anthracite — changes which appear in 

 most cases to be accompanied with deterioration of the coal, physically. 

 The defects of *' crop coal " are well known to all ; but conditions such as 

 cause change of coal in the atmosphere cannot be conceived of as exist- 

 ing at a thousand feet below the surface, where the supply of oxygen is 

 very small and where what suppl}^ there is is fixed very promptly. In 

 fact, there is ground for believing that the changed condition of " crop 

 coal " is due to mechanical even more than to chemical change. 



We can determine one point respecting the time of consolidation- 

 The coal of the Upper Freeport, as well as that of the bed first above it 

 in the Broad Top field, was thoroughly consolidated long prior to the 

 date of folding, for in those beds the fragments were rubbed one on the 

 other until they became as thoroughly polislied and lenticular as are 

 the fragments of Utica slate in the Great valley further east. The 

 Pocono coal near Cliristiansburg, Montgomery county, Virginia, was 

 broken during the folding into irregular pieces, which are wedged together 

 just as are the vastly greater fragments of Pocono sandstone in Wray's 

 hill of Bedford county, Pennsylvania. 



But the whole process of conversion must have been practically com- 

 plete before the rocks were consolidated — indeed, before the coal was 

 buried finally, the result of the pressure being to remove the water and 

 marsh gas and to consolidate the coal. The extent of conversion would 

 depend largely upon the length of time to which the peaty material 

 had been exposed to percolation of water. That practically no further 

 change takes place after burial and consolidation, is suggested by the 

 conditions seen in the Tjaramie coals of New Mexico and Colorado. 

 Within the Trinidad field the coal is anhydrous, rarely containing more 

 than 2 i)er cent of water; but northward from Colorado Springs the 

 coals of the same period have from 12 to 20 per cent, while along the 

 Union Pacific railroad they have from 6 to 13 per cent in Wyoming and 

 from 1.68 to 10.66 in Utah."^ A similar contrast is found between the 



* Marvine : Ann. Report of the U. S. Geol. and Geog. Survey of the Territories for 1873, pp. U2, 113. 



