Post-Grenville orogeny igneous rocks that are unrelated to later orogenies (i.e., anorogenic rocks) make up an important component of the Grenville Province. They commonly consist of small intrusions, but also include the largest mafic pluton in eastern Canada (the Sept Iles complex). Most of the extrusive post-orogenic rocks have now been reworked by the Appalachian orogeny, but a widespread diabase dyke swarm in the western part of the province suggests that a vast area of flood basalts may have been removed by erosion. Most of the post-orogenic rocks are associated with the St. Lawrence rift system which appears to have been active for most of the last 1000 Ma. Post-orogenic rocks may be discovered elsewhere in the province when detailed study is extended beyond the area adjacent to the rift.