162 STEVENSON— INTERRELATIONS OF THE FOSSIL FUELS. , 



several miles, but sooner or later they disappear. In Dakota, the 

 coal is largely wood-like, tough and showing the grain ; flattened 

 trunks of trees frequently differ little from wood except in color. 

 Often, the same seam is composed of alternating layers of tough, 

 brown lignite and of black, lustrous more brittle material. The 

 character of the coal changes toward the west ; in Dakota it is woody 

 and brown, but just beyond the Montana line it is largely lustrous; 

 the same feature was observed still farther west at Glendive. 



Leonard and Smith saw 9 coal beds of workable thickness, the 

 lowest of which, according to Beckly, is about 400 feet above the 

 Glendive bed — at the 'bottom of the Eocene. As result of broader 

 studies, they modify the general assertion of lens-form and assert 

 that some of the important beds have been traced continuously for 

 24 m)iles, while they have been correlated with much certainty for 

 greater distances. Dips are very gentle throughout the region ex- 

 amined. Pockets of lustrous, black, textureless and brittle coal are 

 scattered through many seams and are less pure than the lignite. 



The Eocene coals continue into Canada, where they become less 

 important and are overshadowed by those of the Mesozoic. 



D. White--'^ examined several localities within the Dakota region 

 and gathered material, which was studied microscopically by Thies- 

 sen. The observations are so important that they must be given in 

 full abstract. The coal bed, mined at Wilton, North Dakota, is 

 near the bottom of the Fort Union or early Eocene, a freshwater 

 formation, which stretches, in almost horizontal condition, from 

 central North Dakota westward to the foot of the Rocky Mountains. 

 At Wilton, the floor of the bed is white plastic clay, 4 to 5 inches 

 thick, resting on white sandy clay and occasionally showing large 

 roots in the place of their growth. The thickness of the coal is said 

 to average about 7 feet, with a maximum of 14. The lowest 18 

 inches is a good lignite, broken by very thin clay partings; a half 

 inch parting of mineral charcoal appears at several feet higher. A 

 thin 'bench was seen, consisting of laminated coal, which resembles 

 the bituminous types of Palaeozoic and Mesozoic. The top coal in- 

 cludes a bony bench, formed apparently from dead aquatic or far- 

 decayed vegetation mingled with mineral sediments, and a brownish 



228 D. White, "Origin of Coal," pp. 7-1 1. 



