George Gaylord Simpson 
Fort Union of the Crazy Mountain Field, Montana and Its Mammalian Faunas [PDF ebook] 

Whilst the greatest effort has been made to ensure the quality of this text, due to the historical nature of this content, in some rare cases there may be minor issues with legibility. The second and longer part Of the memoir is zoological and is devoted to definitions of all taxonomic groups which were originally described from this field or the conception of which is markedly affected by material from here, to discussion of the relationships and phylogeny of the mammals represented, and to description Of the specimens in the collection. Geology outside the area Of reference and mammals other than those definitely identified here are mentioned only for the sake of comparison.