118 Cretaceous. 



The Lignitic Group appears, in the valley of the Sonris river, 250 

 miles west of Red river and afibrds numerous sections. The mollusca 

 as well as the characters of the strata show that it is the equivalent 

 of the Fort Union Group. A bed of lignite, 7 feet 3 inches in thick- 

 ness, occurs in the Souris valle^^ about a mile north of the position 

 occupied by the Wood End depot. The sti^ata appear to be nearly 

 liorizontal. West of Wood End, the Souris valley runs north-westward 

 along the base of the Coteau, diverging rapidly from the boundary- 

 line. It loses, at the same time, its abrupt character, and no exposures 

 of the rocks occur for a long distance. In following the 49th parallel, 

 the escarpment of the third great prairie level is overcome, and it is 

 not till after having passed through the broken Coteau belt, and 

 reached the Great Valley, that exposures of the underlying rocks occur. 

 This valley is the most eastern great channel of erosion which crosses 

 the Line southward, toward the Missouri, aod in it the beds of the 

 Lignitic Group are exhibited on a grand scale. On the boundary- 

 line, thus a space of 82 miles, from the 263 to the 345 mile point, is 

 completely shrouded by drift. There is every reason to believe, 

 howcA'er, that the Lignitic Group stretches uninterruptedly between 

 the two localities, and an exposure some distance north of the line 

 sustains this view. 



In the Great Valle^^ the beds exposed are at an elevation of about 

 700 feet greater than those near Wood End, on the Souris river. They 

 consist of shales, clays, and sandstones, with beds of lignite. The 

 next stream crosses the line at the 351 mile point, called Pyramid 

 creek, where the lignite beds are again exposed. They reappear on 

 Porcupine creek, 35 miles farther west, and near the 393 mile point, 

 on the line, an 18 feet bed of lignite occurs. The fossd plants here 

 are nearly identical with those of the Fort Union Group. In the neigh- 

 borhood of Wood Mountain, hard, grayish sandstones, belonging to 

 this group, are exposed, in the sides of the hills and banks of the 

 valleys. At 19 miles from Wood Mountain the edge of the plateau is 

 reached, and a few miles further on, the junction of the lignite with 

 the marine Cretaceous is crossed. Twent}' miles south of the Wood 

 Mountain settlement, on the 49th parallel, near the 425 mile point 

 from Red river, the Lignitic Group is found superimposed upon the 

 marine Cretaceous. The exposures are numerous, and are produced 

 by the sti-eams flowing from the ^southern escarpment of the water- shed 

 plateau, which has been gashed by their action into most rugged Bad 

 Lands. 



This term has attached to it, in the western regions of America, a 



