COALS OF THE ROCKY FORK DISTRICT. 359 



Boulder rivers, have each cut fine sections across the steeply dipping strata 

 forming the northern flanks of the mountain masses toward the south. 



The importance of the Bozeraan field lies not only in the amount and 

 excelleut quality of its coal, but also in its proximity to the Northern Pacific 

 railway ; throughout its entire extent the outcrops of the coal strata are 

 readily accessible and near the main railway line. 



The Rocky Fork district, which was not visited, is very probably an east- 

 erly extension of the Bozeman field, the coal-measures in the western part 

 of the Crow^ reservation being buried beneath an accumulation of volcanic 

 breccias which form the rugged and rough, though not lofty, mountains 

 east of the Boulder river. On this river and its branches the coal-measures 

 cover a considerable area, the seams having a low inclination (10° to 15°) 

 toward the north, so that they could be worked upon an extensive scale. 

 From the Boulder river the coal-measures can easily be traced westward to 

 the border of the great terraced valley of the Yellowstone at Livingston ; but 

 in the western part of their course the seams dip at steep angles (40° to 70°), 

 so that the amount of coal available is not so great as it is farther eastward. 

 Throughout this part of the field there is not a single productive mine; in 

 fact, but few prospect pits. Natural exposures showing a workable thick- 

 ness of coal are, however, not rare. 



West of Livingston the coal lies in folds, due to the three anticlinal axes 

 already mentioned, and the seams usually dip at angles of 50° to 90°. This 

 is, however, the most important part of the field, as all the productive mines 

 are situated in this portiou. For a few miles west of Livingston the coal- 

 measures dip northward at an angle of 40° to 45°, and it is in this portion 

 of the field that the very productive mines of Cokedale are located. A 

 little way west of this town the coal-measures are nearly vertical and the out- 

 crop is S-shaped as the strata bend about the buried end of the first anti- 

 clinal axis ; and there are no productive workings from here to the main divide. 

 West of the anticlinal axis forming this divide the coal strata have been 

 somewhat extensively worked at Timberline, and less extensively at Moun- 

 tainside and Chestnut, where the strata cross the line of the railroad. 



The remainder of the field lies on the eastern flanks of the Bridger moun- 

 tains where the coal measures dip eastward at an angle of about 40°. At 

 present there is not a single productive mine in this part of the field. 



The Horizon of the Coal- Measures. — Seven miles west of Livingston is the 

 little mining town of Cokedale. A north-and-south section, from the high 

 ridge south of this place northward through the coal-measures to the summit 

 of the high ridge north of the railroad, shows the following beds : 



