Slate Islands (Ontario)

The Slate Islands mark the centre of a large meteorite impact crater. The original crater rim is estimated at about 32 km (20 mi) in diameter, but this and most of the crater has subsequently eroded away, leaving the islands which are interpreted as a central uplift. The age of the impact event is estimated to be about 450 million years (Ordovician).^[7][8] Another source estimates the age at 800-500 million years (late Proterozoic to early Paleozoic).^[9]It may be one of several Middle Ordovician meteors that fell roughly simultaneously 469 million years ago, part of a proposed Ordovician meteor event, including the Decorah crater in Iowa, the Ames crater in Oklahoma, and the Rock Elm crater in Wisconsin.^[10]

• http://en.wikipedia.org/wiki/Slate Islands (Ontario)