Greyson Formation

Greenish gray siltite and dark gray argillite with interbedded bands of light brown, sandy argillite and feldspathic quartzite. Thickness as much as 915 m (3,000 ft).
State Montana
Name Greyson Formation
Geologic age Middle Proterozoic
Lithologic constituents
Metamorphic > Metasedimentary > Metaclastic > Argillite
Metamorphic > Metasedimentary > Metaclastic > Metasiltstonesiltite
Metamorphic > Metasedimentary > Metaclastic > Quartzitefeldspathic quartzite

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 Broadwater - Deer Lodge - Gallatin - Jefferson - Judith Basin - Lewis and Clark - Madison - Meagher - Silver Bow