STEVENSON— INTERRELATIONS OF THE FOSSIL FUELS. 185 



variation in percentage of the ash; but it is more apparent when 

 one considers the composition of the ash in the several samples : 



In these coals one has another illustration of indefiniteness of 

 analyses as indications of the actual composition of coal. Nos. 1539 

 and 1 541 have almost the same ultimate composition, yet there is a 

 difference of more than 25 per cent, in the volatile. 



Analyses of coals in the Wyoming-Montana-North Dakota region 

 are numerous. Taff and Wegemann cut samples in the Sheridan and 

 Barber fields. Ten beds were sampled in a vertical section of about 

 1,900 feet. The variations in composition are less than those found 

 within a single bed in the Rockdale area of Texas. The volatile in 

 the lowest bed is 46.30 and that in the highest is 47-67 ; but in one 

 midway in the section it is 44.69, and in the one next above it is 53-20, 

 while in the next to the highest it is only 43-97- The carbon varies 

 from 74.37 in the lowest bed to 70.97 in the highest, but in a bed 

 almost midway in the section it is 71.96. The oxygen is 20.42 in the 

 lowest bed and 22.95 i^i the highest, but is lowest in an intervening 

 bed. The coal throughout this region appears to be remarkably free 

 from inorganic matter, as the ash varies from 4.10 to 9.95 per cent, 

 of the dry coal and it is usually less than 7 per cent.-^^ 



Somewhat farther north, in the Red Lodge field of eastern Mon- 

 tana, samples were cut by Woodruff and were analyzed at the same 

 laboratory. Eight analyses were made of six beds exposed in a sec- 

 tion of approximately 475 feet. The volatile is from 37.35 in the 

 lowest bed to 45.85 in the highest ; but in another analysis, the lowest 

 bed shows 43.35 and the fifth bed, ascending, has but 42.66. The 

 carbon is 72.66 in the lowest and 74.41 in the fifth bed, while in the 



239 U. S. Bureau of Mines, Bull. 22, 1913, pp. 307-309- 



