STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 107 



it is uncertain both as to quantity and quality ; when a seam becomes 

 thick it has much foreign matter and is in great part worthless. 

 Stone could not determine whether or not the Eagle coals are 

 lenses; but the quality is inferior with from 17 to '^^J per cent, of 

 ash. Here, as in districts farther south, the rocks are mostly sand- 

 stone and sandy shale. 



The Lewistown coal field in Fergus County is about 60 miles 

 north-northeast from the ]\Ieagher area and its western limit is near 

 the iioth meridian. Calvert*® found no rocks newer than the Clag- 

 gett, which like the underlying Eagle, consists of sandstone and 

 sandy shale ; cross-bedded sandstones are characteristic. The only 

 coal seam is in the Eagle, at 10 feet from the base. It is merely 

 a coaly layer. Bowen**^ examined the Cleveland field, about 80 

 miles east of north, and the Big Sandy field at an equal distance 

 west of north from Lewistown. In both fields the Judith River 

 and the Eagle are characterized by irregularity of the deposits and 

 the sandstones are often cross-bedded, occasionally ripple-marked. 

 The Eagle becomes shaly in the eastern field. Thin seams of im- 

 pure coal were seen in the Judith River within both fields ; the 

 Eagle has similar streaks in the southern part of Big Sandy but no 

 coal was seen in the northern part of that field nor in the Cleveland 

 field. The Eagle coal is usually bony. 



The Milk River coal field is north from the Cleveland and ex- 

 tends to the Saskatchewan line. Pepperberg^° states that the Judith 

 River coals, all near top of the formation, are lenses, which become 

 thinner and poorer toward the east. The variation in thickness is 

 abrupt ; a lens, 9 feet thick, decreased to a fraction of an inch 

 within a short distance along the outcrop. The quantity of bone 

 is a serious drawback in many mines, so that the product is inferior, 

 because of high ash. The coal is subbituminous and contains min- 

 eral charcoal as well as resins. All deposits in the Judith River 

 are lenticular and the sandstones are locally cross-bedded. Some 

 streaks of coal were seen in the upper part of the Eagle, but they 

 are insignificant. The sandstones of both formations have be- 

 come much less prominent. 



88 W. R. Calvert, Bull. 341, p. no; Bull. 390, pp. 32, 34. 



89 C. F. Bowen, Bull. 541-//, 1914, pp. 45-47, 60-65, 77-So. 



90 L. J. Pepperberg, Bull. 381, pp. 85, 86, 94. 



