| Logan Formation | |
| Type: | Sedimentary |
| Period: | Mississippian |
| Prilithology: | sandstone, siltstone, conglomerate |
| Otherlithology: | shale |
| Namedfor: | Logan, Ohio |
| Namedby: | Andrews, 1870 |
| Region: | Appalachian Basin |
| Country: | United States |
| Unitof: | Waverly Group |
| Subunits: | Berne, Byer, Allenville, Vinton |
| Underlies: | Maxville Limestone, Pottsville Group, and Rushville Shale |
| Overlies: | Cuyahoga Formation |
| Thickness: | 0 to 40 m |
| Extent: | Ohio, West Virginia |
The Logan Formation is the name given to a Lower Carboniferous (early Osagean) siltstone, sandstone and conglomeratic unit exposed in east-central Ohio and parts of western West Virginia, USA.
The Logan Formation was named by Andrews (1870) and originally described as a "buff-colored, fine-grained sandstone" above the Waverly Formation and below the Maxville Limestone. Bork and Malcuit (1979) concluded that the Logan Formation was deposited on a shallow marine shelf in a generally transgressing sea. The age of the Logan Formation has been established as early Osagean (Tn3) by the occurrences of brachiopods, ammonoids, conodonts and miospores (Clayton et al., 1998; Matchen and Kammer, 2006).