erc: who: Kalliokoski, Jorma O. what: Uranium, Thorium, and Potassium Content of Precambrian Rocks, Upper Peninsula of Michigan and northern Wisconsin when: 19770200 where: https://digital.library.unt.edu/ark:/67531/metadc958187/ erc-support: who: University of North Texas Libraries what: Permanent: Stable Content: when: 20081203 where: https://digital.library.unt.edu/ark:/67531/