216 DOUGLASS — CRETACEOUS AND LOWER TERTIARY. [AprU3, 



Fort Union. What is supposed to be Laramie in the present sec- 

 tion is very thick, probably approximating that of Lindgren's 

 measurements. But here, as everywhere else, the boundaries of the 

 Laramie are uncertain. Here, however, we have it confined be- 

 tween certain limits. We have below a characteristic Fort Pierre 

 fauna and above a characteristic Fort Union flora. Just how much 

 of that which intervenes is Laramie is not known. I have no 

 doubt that here deposition was going on at the same time as that of 

 not only the Livingston, but also of the Arapahoe and Denver beds. 

 Whether these beds will ultimately be assigned to the Upper Lara- 

 mie, or included in a separate formation, depends upon the results 

 of future careful investigation. 



Tertiary. 



Fort Union. 



The dark shales just mentioned continue upward, changing little 

 in character ; but brown concretions become numerous, then layers 

 containing shells of bivalve MoUusca, then occasional layers of 

 sandstone, and above these, often capping the bluffs, heavy gray 

 sandstones, usually hard, sometimes laminated and sometimes mas- 

 sive. Above this I cannot speak definitely, but think that the Fort 

 Union continues much higher. The strata from the top of the bluffs 

 south of Fish Creek, which make a bench sloping toward Sweet- 

 grass Creek in the direction of Melville, perhaps belong to higher 

 members of this formation. The strata are not always continuous 

 for great distances, but vary locally ; yet a general description can 

 be given that will apply fairly well to the beds examined. There 

 are dark gray shales that in many places weather to thin, flaky 

 particles on the surface. The wind blows away this light material 

 and leaves bare depressions without vegetation. The sandstones 

 are usually hard, sometimes massive or imperfectly bedded, and in 

 some places break into great blocks, which tumble down the steep 

 sides of the bluffs. 



In the Fish Creek region these heavy sandstones, which lie above 

 the soft shales, form a long line of rugged bluffs extending along 

 the south side of the creek from the neighborhood of Porcupine 

 Butte eastward for twenty-five or thirty miles \ then it extends 

 southeastward, probably forming the divide between the Sweetgrass 

 on the southwest and the southern branches of Fish Creek and Big 



