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Spokane shale

Spokane shale: red or red-purple shale with numerous green beds locally and some quartzite; grades into the Empire above and the Greyson below and in some areas as mapped probably includes all or part of Empire and Greyson shales. The name has been used over a wide area in Montana, but in a strict sense can be used safely only in the general vicinity of Helena.
State Montana
Name Spokane shale
Geologic age Proterozoic | Mesoproterozoic
Primary rock type meta-argillite
Secondary rock type quartzite
Other rock types limestone
Lithologic constituents
Major
Metamorphic > Metasedimentary > Metaclastic > Argillite (Greenschist)
Minor
Metamorphic > Metasedimentary > Metaclastic > Quartzite (Greenschist)
Incidental
Sedimentary > Carbonate > Limestone (Bed)Weakly metamorphosed limestone.
Map references
Ross, P.R., Andrews, D.A., and Witkind, I.J., 1955, Geologic map of Montana: U.S. Geological Survey, 2 sheets, scale 1:500,000.
Unit references
Ruppel, E.T., O'Neill, J.M., and Lopez, D.A., 1993, Geologic map of the Dillon 1o x 2o quadrangle, Idaho and Montana: U.S. Geological Survey Miscellaneous Investigations Series Map I-1803-H, scale 1:250,000.
Lewis, R.S., 1998, Preliminary geologic map of the Butte 1° x 2° quadrangle: Montana Bureau of Mines and Geology Open File Report 363, 16 p, scale 1:250,000.
McGrew, L.W., 1977, Geologic map of the Ringling quadrangle, Meagher County, Montana: U.S. Geological Survey Geologic Quadrangle Map 1382, scale 1:24,000.
Tysdal, R.G., Ludington, Steve, and McCafferty, A.E., 1996, Mineral and energy resource assessment of the Helena National Forest, west-central Montana: U.S. Geological Survey Open-File Report 96-683-A, 322 p., 6 plates.
Skipp, Betty and McGrew, L.W., 1977, The Maudlow and Sedan Formations of the Upper Cretaceous Livingston Group at the west edge of the Crazy Mountains basin, Montana, in Contributions to stratigraphy: U.S. Geological Survey Bulletin 1422-B, p.
Wilson, A.B., and Elliott, J.E., 1997, Geologic maps of western and northern parts of Gallatin National Forest, south-central Montana: U.S. Geological Survey Geologic Investigations Series Map I-2584, 2 sheets, scale 1:126,720.
Mudge, M.R., Earhart, R.L., 1983, Geologic and structure maps of the Choteau 1° x 2° quadrangle, western Montana: United States Geological Survey Miscellaneous Geologic Investigations Series Map I-1300, scale 1:250,000.
Harrison, J.E., Whipple, J.W., and Lidke, D.J., 1998, Geologic map of the western part of the Cut Bank 1° x 2° quadrangle, northwestern Montana: U.S. Geological Survey Miscellaneous Geologic Investigations Series Map I-2593, scale 1:250,000.
McMannis, W.J., 1955, Geology of the Bridger Range, Montana: Geological Society of America Bulletin, v. 66, no. 11, p. 1385-1430.
Harrison, J.E., Griggs, A.B., and Wells, J.D., 1986, Geologic and structure maps of the Wallace 1° x 2° quadrangle, Montana and Idaho: Montana Bureau of Mines and Geology Montana Atlas Series 4-A, scale 1:250,000.
Harrison, J.E., Cressman, E.R., and Whipple, J.W., 1992, Geologic and structure maps of Kalispell 1° x 2° quadrangle, Montana and Alberta, British Columbia: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-2267, scale 1:250,000.
Harrison, J.E., 1972, Precambrian Belt basin of northwestern United States--Its geometry, sedimentation and copper occurrences: Geological Society of America Bulletin, v. 83, no. 5, p. 1215-1240.
Skipp, Betty, and Peterson, A.D., 1965, Geologic map of the Maudlow quadrangle, southwestern Montana: U.S. Geological Survey Miscellaneous Investigations Series Map I-452, 2 sheets, scale 1:24,000.
Earhart, R.L., Mudge, M.R., and Connor, J.J., 1984, Belt Supergroup lithofacies in the Northern Disturbed Belt, northwest Montana, in McBane, J.D., and Garrison, P.B., eds., Northwest Montana and adjacent Canada--Montana Geological Society 1984 Field Con
Counties Broadwater - Gallatin - Jefferson - Lewis and Clark - Meagher - Powell