Swift Formation

Orangish brown, glauconitic, flaggy-bedded, commonly fossiliferous, fine-grained sandstone or sandy coquina with subordinate dark gray shale interbeds; chert pebbles common. In west-central and northwestern Montana, a dark gray, noncalcareous, micaceous shale forms the lower part of the formation, commonly with a basal chert-pebble conglomerate or conglomeratic sandstone as much as 3 m (10 ft) thick. Shallow marine. Thickness as much as 70 m (230 ft).
State Montana
Name Swift Formation
Geologic age Jurassic
Lithologic constituents
Major
Sedimentary > Clastic > Mudstone > Shale (Bed)
Sedimentary > Clastic > Sandstone (Bed, Glauconitic)
Minor
Sedimentary > Clastic > Conglomerate (Bed)
Incidental
Sedimentary > Clastic > Mixed-clastic > Conglomerate-sandstone (Bed)
Sedimentary > Chemical > Chert (Bed)
Sedimentary > Carbonate > Limestone > Coquina (Bed)sandy coquina
References

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 Beaverhead - Big Horn - Blaine - Fergus - Phillips