160 STEVENSON— INTERRELATIONS OF THE FOSSIL FUELS. ■ 



broken by many partings and the coal, more or less laminated, is 

 jointed. 



A small area examined by Rogers--'' is farther northeast ; there 

 the more indurated rocks of the lower division show mud cracks, 

 cross-bedding and rippled surfaces. The coal of that division is 

 brittle and fairly compact, though in some cases the woody texture 

 ■is distinct. The coal of the upper division is mostly lignitic ; but 

 this distinction is not absolute, for vitreous coal is found in some of 

 the higher beds and woody lignite is by no means uncommon in the 

 lower division. Throughout, the coal beds are irregular ; in all parts 

 of the section, beds thin out and others appear at 8 or lo feet higher 

 or lower, so that Rogers is compelled to recognize horizons rather 

 than contemporaneous separate deposits. 



Farther eastward, beyond the Yellowstone River, one reaches 

 the great lignite area w'ith its numerous independent basins, which 

 were examined by Bowen, Herald, Vance, Stebinger and Beckly.--*' 

 The southern or Baker field shows mostly lignitic coal, woody in 

 structure, brown and tough ; the beds are broken by partings of con- 

 siderable thickness and the benches are seldom of workable thick- 

 ness. In the Terry field, all the deposits are irregular; the coal beds 

 vary abruptly in thickness and character, often changing from coal 

 to shale within a few yards. Even the comparatively persistent bed 

 at the base is so irregular that Herald is inclined to speak of it as 

 a " lignitic zone." The lens-like form of the deposits is character- 

 istic throughout. The Glendive area is somewhat farther north. 

 The lowest coal bed is apparently continuous along an outcrop of 

 150 miles, but Hance found it extremely variable in thickness and 

 quality. Its coal is inferior to that of the bed, 50 to 150 feet higher. 

 In places, two sets of joints are distinct. 



Stebinger, after study of the Sydney field, which extends to the 

 Canadian border, was not willing to admit that the lens-form is a 

 persistent feature, though he recognizes fully the abrupt and ex- 



"^ G. S. Rogers, " The Little Sheep Mountain Coal Field," U. S. Geol. 

 Survey, Bull. 531 F, 1913, pp. 9, 11, 19, 20, 23, 24. 



226 " Lignite in Montana," U. S. Geol. Survey, Bull. 471 D, 1912 ; C. F. 

 Bowen, pp. 21, 38, 39; F. A. Herald, pp. 56. 60, 62, 78; J. H. Vance, pp. 89, 92, 

 97, 98; E. Stebinger, pp. 106, 107, 115; A. L. Beckley, 152. 



