CoachA peneplain is a land surface of low relief, near the base level of erosion, cut across rocks of different hardness and structure by long erosion of a former relief.
| phase | age | what collided |
|---|---|---|
| Penobscotian | 490–485 Ma | an island arc thrust onto the Avalonian margin |
| Grampian, Taconian | 480–455 Ma | island arcs against Laurentia (Scotland; the northern Appalachians) |
| Shelveian | early Late Ordovician | Avalonia against Baltica; the Tornquist Sea closes |
| Scandian | 425–400 Ma | Baltica against Laurentia; the great nappes of Scandinavia |
| Acadian | Early Devonian | terranes from Gondwana against the new continent; Iapetus closed |