Upper Prichard or Appekunny Formation

Upper Prichard Formation: Black and gray, pyritic siltite and argillite in planar couplets. Appekunny Formation: Gray and greenish gray argillite interbedded with light gray quartzite. Thickness as much as 1,700 m (5,577 ft).
State Montana
Name Upper Prichard or Appekunny Formation
Geologic age Middle Proterozoic
Lithologic constituents
Metamorphic > Metasedimentary > Metaclastic > Metasiltstonesiltite
Metamorphic > Metasedimentary > Metaclastic > Quartzite
Metamorphic > Metasedimentary > Metaclastic > Argillite

Vuke, S.M., Porter, K.W., Lonn, J.D., and Lopez, D.A., 2007, Geologic Map of Montana - Compact Disc: Montana Bureau of Mines and Geology: Geologic Map 62-C, 73 p., 2 sheets, scale 1:500,000. This map was digitized in 2012 as a result of a contract between the U.S. Geological Survey and the Montana Bureau of Mines and Geology.

NGMDB product
Counties Flathead - Glacier - Lake - Lewis and Clark - Lincoln - Mineral - Missoula - Powell - Sanders