110 Cretaceous. 



near Bear river, in "Western Wyoming, lie regarded as of the 

 same age as the Coalville series. His section here is 3,542 feet thick. 

 The lower 1,213 feet he regarded as certainly Cretaceous, the next 

 2,049 feet he thought is probabl}^ Cretaceous, and the upper 280 feet he 

 regarded as of Tertiary age. 



The Bitter -creek series, which is found along Bitter creek (a small 

 tributary of Green river, in Wyoming), from Black Butte northwest- 

 ward to Salt Wells Station, on the Union Pacific Railroad, and at 

 Rock Spring, and some other points west of Salt Wells, consisting of a 

 vast succession of rather soft, light-N'ellowish, lead-grey, and whitish 

 sandstones, with seams and beds of various colored clays, 

 shale, and good coal, the whole attaining an aggregate thick- 

 ness of more than 4,000 feet, present a mingling of fresh, brackish, and 

 salt water tj^pes of invertebrate fossils, such as Goniobasis, Viviparus, 

 Corbicula, Corhnla, Ostrea, Anomia, and Modiola. This is the Lig- 

 nitic Group which Prof. Lesquereux determined from the character of 

 the plants to be of Eocene age, and Prof. Cope, from the Diuosaurian 

 remains, to be of Cretaceous age. Prof. Meek thought the Judith 

 river brackish-water beds are of the same age, and that the inverte- 

 brate fossils alone left the question of the age of the series in doubt. 

 He stated the information as to its age in the following summary: 

 • 1. That it is conformable to an extensive fresh-water Tertiary for- 

 mation above, from which it does not differ materialh' in lithological 

 characters, excepting in containing numerous beds and seams of coal. 



2. Tiiat it seems also to be conformable to a somewhat differentl}' 

 composed group of strata (1,000 feet or possibly much more in thick- 

 ness) below, apparently' containing little if any coal, and believed to be 

 of Cretaceous age. 



3. That it shows no essential difference of lithological characters 

 from the Cretaceous coal-bearing rocks at Bear river and Coalville. 



4. That its entire group of vegetable remains (as determined by 

 Prof. Lesquereux) presents exclusiA^elj' and decidedly' Tertiary af- 

 finities, excepting one peculiar marine plant {Ilalymenites).^ which also 

 occurs thousands of feet beneath undoubted Cretaceous fossils, at 

 Coalville, Utah. 



5. That all of its animal remains, j^et known, are specifically different 

 from any of those hitherto found in any of the other formations of 

 this region, or, with perhaps two, or possibly three exceptions, 

 elsewhere. 



6. That all of its known invertebrate remains are mollusks, con- 

 sisting of about thirteen species and varieties of marine, brackish and 



