| Colonsay Group | |
|---|---|
| Stratigraphic range: Neoproterozoic | |
 Smaull Greywacke Formation, near Rubha Lamanais, Rinns of Islay | |
| Type | Group |
| Lithology | |
| Primary | Sandstone |
| Other | Shale, siltstone |
| Location | |
| Region | Inner Hebrides |
| Type section | |
| Named for | Colonsay |
The Colonsay Group is an estimated 5,000 m thick sequence of mildly metamorphosed Neoproterozoic sedimentary rocks that outcrop on the islands of Colonsay, Islay and Oronsay and the surrounding seabed. They have been correlated with the Grampian Group, the oldest part of the Dalradian Supergroup.