1. Big Snowy and Amsden Groups and the Mississippian-Pennsylvanian boundary in Montana, Author/Creator: Maughan, Edwin K., 1926-1995 Publication/Creation: Washington : U.S. Govt. Print. Off, 1967 Resource Type: Book Is Part Of: U.S. Geological Survey professional paper, no. 551-554. Access & Availability: Loading