ORIGIN OF THE PENNSYLVANIA ANTHRACITE. 679 



as at the north, to the general elevation of the synclines and 

 their passage into the New York plateau. 



Analyses of coal samples, taken from the Pittsburgh bed in 

 the several basins, show a progressive decrease in the proportion 

 of volatile, combustible matter toward the east or southeast, a 

 fact which early attracted the attention of H. D. Rogers, and 

 which has possessed much interest for geologists ever since. 

 Analyses made for the Second Pennsylvania Survey prove the 

 same condition in the lower coals. Mr. Winslow's studies of 

 the Arkansas coals show a similar tendency to decrease in the 

 same direction ; and Murchison discovered a like condition in 

 the Donetz anthracite field of southern Russia. 



H. D. Rogers, 1 in 1842, announced to the Association of 

 American Geologists the law of gradation, as he understood it, 

 which involves "a progressive increase in the proportion of the 

 volatile matter, passing from a nearly total deficiency of it in 

 the driest anthracites to an ample abundance in the richest 

 caking coal." Finding, as he believed, that the volatile matter 

 in the coal augments westwardly, precisely as the flexures 

 diminish, he attributed the variation to the influence of steam 

 and other intensely heated gases escaping through crevices 

 necessarily produced during the permanent bending of the 

 strata. Under such conditions, the coal throughout the eastern 

 basins, the more disturbed, would discharge more or less of the 

 volatile constituents during the violent earthquake action, 

 whereas the more western beds, less disturbed, would be less 

 debituminized. 



J. J. Stevenson, 2 in 1877, showed that the variations in 

 volatile exhibited by the Pittsburgh coal bed along the south- 

 east and northwest line bear no relation whatever to increase or 

 decrease of stratigraphical disturbance, and suggested that the 

 variations are due to difference of conditions under which the 

 coal was formed. 



'Rogers: Reps, of the 1st, 2d and 3rd meetings of the Association of American 

 Geologists and Naturalists. 1843, pp. 470 et seq. 



2 Stevenson: 2d Geol. Surv. of Penn., Rep. of Progress on the Fayette and 

 Westmoreland Dist. Pt. I. pp. 61, et seq. 



