II. VERTEBRATE FOSSILS FROM THE FORT UNION 



BEDS. 



By Earl Douglass. 



In the autumn of 1901 the present writer made a small collection of 

 fossil plants, mollusca, and vertebrates in the Fort Union beds at Bear 

 Butte, in Sweetgrass County, Montana. The fossil plants were sent 

 to Professor Frank H. Knowlton for identification, and the mammals 

 were described by myself.^ 



Bear Butte is a mesa-shaped hill east of Widdecombe Creek on the 

 John and William Widdecombe ranch ("Jack and Bill Ranch"), 

 from sixteen to eighteen miles northeast of Melville, in the northern 

 part of SAveetgrass County. A mile or more farther north Widde- 

 combe Creek flows into Fish Creek. The butte is really a portion of 

 the bench land or plateau, lying farther to the southwest, from which 

 it is partly separated by erosion. 



On the north and east sides of the northern portion of Bear Butte, 

 the more nearly level surface which skirts its steeper portion is com- 

 posed of dark clay-shales which disintegrate and weather into flaky 

 particles. In places the wind and water carry away these particles, 

 leaving small areas bare of vegetation. Below these shales are hard, 

 thin-layered sandstones. These belong to division " E " of the " Lar- 

 amie and Doubtful Laramie " described in another paper to be shortly 

 published. Above these nearly pure shales, near the northern foot of 

 Bear Butte, the shales contain ferruginous concretions, and there are 

 thin lenses, bands, or layers of sandstone. The sandstones sometimes 

 contain impressions of leaves, and in the limestones are fossil clams 

 and bones and teeth of mammals and reptiles (crocodiles and champ- 

 sosaurus). The shales which are known to be of Lower Tertiary age 

 are, I think, not less than too feet in thickness. The thickness of this 

 whole series of shales is probably more then 400 feet, and it may all 

 be Tertiary. Within 10 or 15 feet of the top they contain impressions 

 of plants. Just above the shales, at least on the western side of the 



' '* A Cretaceous and Lower Tertiary Section in South Central Montana," Proc. 

 Atner. Philos. Soc, Vol. XLI, No. 170, April, 1902. 



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