The Blakely Sandstone is a Middle Ordoviciangeologic formation in the Ouachita Mountains of Arkansas and Oklahoma. First described in 1892,[3] this unit was not named until 1909 by Albert Homer Purdue in his study of the Ouachita Mountains of Arkansas. Purdue had initially named this unit the Caddo Shale at a 1907 Geological Society of America meeting,[4] but later redefined and renamed the unit as the Ouachita Shale.[5] He again renamed the unit to the Blakely Sandstone in a letter to Edward Oscar Ulrich, to which Ulrich used in a 1911 publication, becoming the first reference using this name.[2] Ulrich assigned the Blakely Mountain in Garland County, Arkansas as the type locality, but did not designate a stratotype. As of 2017, a reference section for this unit has yet to be designated.
^McFarland, John David (2004) [1998]. "Stratigraphic summary of Arkansas"(PDF). Arkansas Geological Commission Information Circular. 36: 19. Archived from the original(PDF) on 2016-12-21. Retrieved 2018-01-08.
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