198 white: relations between coal and petroleum 



friction heat of molecular displacement caused by the stresses 

 of intermittent thrusts of progressive intensity was generated 

 throughout such an enormous thickness of rocks and through so 

 great an area as to produce sensible temperatures under con- 

 ditions necessitating long periods for their dissipation. 



The effectiveness of thrust pressure as the cause of regional 

 coal alteration is well illustrated in most large areas of high rank 

 coal, but in no part of the world is it more clearly demonstrated 

 than in the great Appalachian coal field. To show in a general 

 way the progress of the regional alteration in this area, I have, 

 in preparing the accompanying map, first platted the ''fixed 

 carbon" (pure coal basis) of the coals at the localities from which 

 samples have been analyzed. ^^ Lines were then drawn through 

 the points of equal fixed carbon (or volatile matter). Such 

 lines, which were termed ''isoanthracitic" lines by Strahan^^ 

 and Pollard, and which I have termed "isovols," are drawn to 

 mark each 5 per cent of increase in the fixed carbon in the pure 

 coal. The degree of accuracy of the representation will not 

 here be discussed. The "contouring" of the fixed carbons is 

 subject to minor revision. 



A glance at the Appalachian coal field in this map shows the 

 position of the lowest rank coals to be in the western portion 

 of the area, while the highest rank coals, the anthracites, are 

 found at the extreme eastern border. The isovols show both 

 the extent of the alteration of the coals and the regional pro- 

 gressive character of that alteration toward the Atlantic; that 

 is, in the direction from which the great isostatic Appalachian 

 thrusts are known to have come. Small areas of coal with 

 slightly higher fixed carbon indicate, in most cases, points of 

 locally greater, perhaps of cumulative, stresses, while "islands" 

 of low fixed carbon probably mark areas of corresponding partial 

 immunity. The more important thrust faults, lying within or 



" The use of the fixed carbons, though less satisfactory on the whole than 

 the C-0 ratios of the dry coals, makes it possible to employ tlic great volume of 

 proximate analyses illustrating coals in far greater geographical extent and 

 completeness of representation. In the regions of lower rank coals, it is neces- 

 sary to use some other method to show satisfactorily the rank of the fuels. 



15 The Coals of South Wales Coal Field, p. 72. 



i 



