| Scales Shale | |
| Type: | Formation |
| Age: | Ordovician |
| Period: | Ordovician |
| Region: | Illinois, Indiana |
| Country: | United States |
| Unitof: | Maquoketa Group |
| Underlies: | Fort Atkinson Limestone |
| Overlies: | Trenton Limestone |
The Scales Shale is a geologic formation in Illinois. It preserves fossils dating back to the Ordovician period.