LVIII INTRODUCTORY REMARKS. 



and New Mexico, like the Vancouver coals, are unquestionably of Cretaceous 

 age, as if this goes to show that all of the others must also belong to the 

 same. On the other hand, others, who would make them all Tertiary, refer 

 to the Evanston and Carbon station mines in Wyoming, and try to ignore 

 the unmistakable evidences of the Cretaceous age of the lignites at other 

 places, as if those evidences are merely exceptional and dubious. 



In regard to the relations of the Fort Union group to the Lignite 

 formations along the eastern base'of the Rocky Mountains, through Colorado 

 into New Mexico, from which Professor Lesquereux has identified some of 

 the Upper Missouri Fort Union group plants, the author can express no 

 opinion of his own, never having seen a single species of the Fort Union 

 group invertebrates from the strata including the lignite beds at any of these 

 more southern localities. A single species, however, from the coal-bearing 

 strata at Carbon station on the Union Pacific Railroad is probably identical 

 with Viviparus trochiformis from the Fort Union group; but the specimen 

 is imperfect, and may belong to an allied species. 



As already shown, all of the species of invertebrates yet known from 

 the extensive lignite series along Bitter Creek, farther westward in Wyo- 

 ming, are clearly distinct from Fort Union group forms; and consequently 

 these Bitter Creek beds cannot be placed on the same horizon with the Fort 

 Union group, on any evidence to be derived from their known invertebrate 

 remains. 



Yet it is an interesting fact that among Lieutenant Wheeler's collections 

 from Southern Utah, Dr. White has figured the following Upper Missouri 

 Fort Union group species, viz, Viviparus trochiformis, Goniobasis Nebrascensis, 

 and G. tenuicarinata, from beds referred by all explorers of that region to the 

 Tertiary, and possibly representing the Fort Union group.* 



The Fort Union group occupies a large area of country in the l'egion 

 of Fort Union, on the Missouri, and below to Fort Clarke, and beyond on the 

 higher country. From Fort Union it extends southward in a broad belt across 

 the Yellowstone, between the Black Hills and Big-Horn Mountains, to where 

 it was found by Dr. Hayden passing beneath the White River group about 

 sixty miles north of Fort Laramie. It also extends northward into the Brit- 

 ish possessions, many of its characteristic fossils having been discovered by 



* See Dr. White's Report on Lieutenant Wheeler's Collections, pi. xxi. 



