542 " !'i.(ii;a of iiii; lakamik (jRori'. 



COLLECTIONS FROM THE FORT UNION GROUP. 



The several localities from wliich the principal collections made in 

 the season of 1883 were obtained lio alonji; the Yellowstone Kiver, above 

 and below the town of Glendive, which is sitnated three miles above 

 old Fort Glendive and on the opposite or right bank of the river, at 

 the point where the Northern Pacific Railroad first enters the valley 

 from the east. Sntlicieutly precise descriptions of the geographical 

 position of each of these beds were given in my administrative re- 

 port for that year, and these need not be repeated. 



The several beds worked for fossils represent, I am convinced, a num- 

 ber of qnite distinct epochs separated far enough in time to have al- 

 lowed important changes in the vegetation to take place. The locali- 

 ties are not far enough apart geographically to account for the great 

 differences in the diflerent Morulas, the extreme distance between the 

 remotest beds not exceeding fifty miles. There were only two of the 

 beds that I was tolerably well satisfied were actually synchronous, and 

 these were among the most remote from each other. These beds are 

 those of Iron Bluff and Burns's Ranch. The plant-bearing stratum at 

 Iron Bluff is situated about fifty feet above the level of the river at low 

 water, while that at Burns's Ranch is at the very water's edge and a 

 few feet above and below. If the beds at Burns's Ranch represent a 

 simple continuation of the strata that apjiear at Iron Bluff, the dip to 

 the north must be somewhat greater than the natural tall in the river, 

 but the distance is about forty miles. Between Iron Bluff and Glendive, 

 however, there occurs an outcrop of marine Cretaceous strata, contain- 

 ing characteristic Fox Hills shells. This forms an anticlinal of some five 

 orsix miles along the right bank of the Yellowstone,and again disai)pears 

 beneath true Laramie strata some distance above the town. On the side 

 toward Iron Bluff the Cretaceous seems to lie entirely below the rail- 

 road cutting at the base of the bluff, but the talus of red blocks of fer- 

 ruginous baked marl obscured this portion and i)revented its study. 

 This is the only outcrop of Cretaceous rocks in the entire district visited 

 by me. 



The reasons for regarding the Iron Bluff and Burns's Ranch beds as 

 equivalent are chiefly paleontological. The characteristic plant of the 

 Iron Bluff strata was the large cordate leaf which I have designated as 

 Coceulus Tl(n/deniaHHS. This occurs also at Burns's Ranch and has been 

 found only in these two localities. The characteristic plant of the 

 Burns's Rancli locality is Trapa microphylla, and this also occurs at 

 Iron Bluff and at no other place in the Fort Union group. The remark- 

 able Cryptogam mentioned above occurs in both beds and several of 

 the celastroid leaves are common to the two localities. jSToue of the 

 forms found at these two localities occur at any of the others. The 

 rock difl'ers greatly in appearance, but this difl'erence is mainly due to 

 the former having been sulyected to heat, its carbon driveu out, and 



