Theodosia Formation

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| name = Theodosia Formation

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| type = Formation

| age = Ordovician

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| namedfor = Theodosia, Ozark County, Missouri

| namedby = James Shelley Cullison{{cite journal|last1=Cullison|first1=J.S.|title=The stratigraphy of some Lower Ordovician formations of the Ozark uplift|journal=University of Missouri School of Mines and Metallurgy Bulletin, Technical Series|date=1944|volume=15|issue=2|pages=7, 11, 15, 16, 17, 21, 23, 25–32, pl. 2}}

| region = Arkansas, Missouri

| country = United States

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The Theodosia Formation is a geologic formation in Missouri. It preserves fossils dating back to the Ordovician period.

The Rich Fountain Formation was proposed in 1944 as the equivalent of the lower part of the Jefferson City Formation in a new Jefferson City Group. The Theodosia Formation was proposed as the equivalent of the upper Jefferson City and the lower portion of the overlying Cotter Formation.[http://www.dnr.mo.gov/geology/geosrv/ogc/docs/RI-073.pdf Thompson, Thomas L., 2001, Lexicon of Stratigraphic Nomenclature in Missouri, Missouri Department of Natural Resources, Division of Geology and Land Survey, Report of Investigation Number 73, p 239 and 287] This formation was also proposed for use in Arkansas by the original author of the name, but it was never used by other workers in Arkansas.