FORT UNION" OF CRAZY MOUNTAIN FIELD, MONT. 



17 



Bear 



Hell 

 Creek 



Zone of hard brown concretions, with numerous fresh-water in- 

 vertebrates and some turtle bones ±1 



Transitional beds with shales somewhat darker than those below 



and with local lenses of brown sandstone 15 



Alternating white cross-bedded sandstones and pale shales. .about 485 



about 500 

 Softer beds, pale sandstone and clay, with dinosaurs. _ (Not measured) 



Definition of the new name "Bear" is given on page 20. 



All these beds are tilted here, but there is no evidence of angular 

 unconformity. The contact beneath the lowest hard sandstone of the 

 Bear is sharp but not more so than beneath other sandstones through- 

 out this series. Such a contact could, but does not necessarily, 

 represent a parallel or erosion al disconformity. The change from 

 Hell Creek to Bear is, however, rather more abrupt than from Bear 

 to Fort Union No. 1, the latter being transitional through a thickness 

 of 15 to 20 feet, the boundary here taken by convention at a local shell 

 lens. 



Dinosaurs are found in place, apparently as originally deposited, at 

 almost all levels in the Hell Creek, although no very good specimens 

 have been foimd in this field. I have seen no dinosaurs in the Bear, 

 but Mr. Silberling informs me that he has found isolated, rare, and 

 very fragmentary specimens in the lower part of that formation, the 

 highest being 80 feet above the base in this section. It is entirely 

 possible that these few fragments were redeposited and derived from 

 the Hell Creek. No dinosaurs have been found in the upper 420 feet 

 of the Bear, but a few champsosaur and turtle bones and some in- 

 vertebrates occur. 



Invertebrates from the lens here considered as marking the top of 

 the Bear have been identified by Dr. L. S. Russell as follows: 



IFusconaia danae (Meek and Hayden). 

 'iNedionidus senectus (White). 

 Elli-ptio priscus (Meek and Hayden). 

 Viviparus trochiformis (Meek and Hay- 

 den). 



Viviparus formosus Meek. 

 Campeloma nehrascense whitei Russell. 

 Campeloma limnaeiforme (Meek and 



Hayden). 

 Physa cf. canadensis Whiteaves. 



Dr. Russell remarks that the three pelecypods range widely in the 

 Northwest, Judith River to Fort Union, and that the species of Vivi- 

 parus characterize the Fort Union and equivalents (listing mainly 

 Upper Paleocene levels), the two Campelomas are likewise from the 

 Fort Union or equivalents, and the Physa is of little significance. He 

 concludes that the "fauna contains nothing characteristic of the Lance 

 and includes several species restricted to the Fort Union. It can be 

 regarded with some confidence as Paleocene in age." 



