Ordovician rocks

Mainly black to gray slate or slaty argillite, argillite, black to dark-gray siltstone in north-central Stevens County and grayish olive-green silty argillite in west-central Stevens County. Many occurrences of Early and Middle Ordovician graptolites; also rare conodonts.
State Washington
Name Ordovician rocks
Geologic age Middle Ordovician
Lithologic constituents
Metamorphic > Metasedimentary > Metaclastic > ArgilliteIncludes calcareous and siliceous argillite.
Metamorphic > Metasedimentary > Metaclastic > SlateIncludes carbonaceous slate.
Sedimentary > Clastic > Siltstone (Bed)Also referred to as siltite (Joseph, 1990a, b).
Metamorphic > Metasedimentary > Metaclastic > PhylliteAbundant in large outcrop west of the Columbia River but not present in Ledbetter Slate (Joseph, 1990a).
Metamorphic > Metaigneous > GreenstoneJust west of Columbia River (Yates, 1964).
Sedimentary > Carbonate > Limestone (Bed)Uppermost beds of Ledbetter Slate are black limestone, west-central Stevens County (Park and Cannon, 1943).
Metamorphic > Metasedimentary > Metaclastic > Quartzite15 ft. black quartzite band in Ledbetter Slate, west-central Stevens County (Park and Cannon, 1943). Possibly minor in rank but less abundant than siltstone or phyllite.
Comments Ledbetter Slate is 1200 m. thick in Nespelem Quadrangle, west Stevens County (Joseph, 1990b). Stoffel and others, 1991, report that while the term "Mission argillite" was once widely used, it has since been abandoned.
Stratigraphic units Ledbetter Slate; Mission argillite (in part)

Huntting, M.T., Bennett, W.A.G., Livingston, V.E.Jr., and Moen, W.S., 1961, Geologic Map of Washington: Washington Division of Mines and Geology, scale 1:500,000.

Park, C.F.Jr., and Cannon, R.S.Jr., 1943, Geology and Ore Deposits of the Metaline Quadrangle, Washington: U. S. Geological Survey Professional Paper 202, 81 p.

Weaver, C.E., 1920, The Mineral Resources of Stevens County: Washington Geological Society Bulletin No. 20, 350 p.

Stoffel, K.L., Joseph, N.L., Waggoner, S.Z., Gulick, C.W., Korosec, M.A., Bunning, B.B., 1991, Geologic Map of Washington--Northeast Quadrant: Washington Division of Geology and Earth Resources Geologic Map, GM-39, scale 1:250,000.

Joseph, N.L., 1990a, Geologic Map of the Colville 1:100,000 Quadrangle, Washington-Idaho: Washington Division of Geology and Earth Resources Open File Report 90-13, 78 p., 1 pl.

Joseph, N.L., 1990b, Geologic Map of the Nespelem 1:100,000 Quadrangle, Washington: Washington Division of Geology and Earth Resources Open File Report 90-16, 47 p., 1 pl.

Yates, R.G., 1971, Geologic Map of the Northport Quadrangle, Washington: U. S. Geological Survey Miscellaneous Geologic Investigations Map I-603, scale 1:31,680.

NGMDB product
Counties Ferry - Pend Oreille - Stevens