Minerals with ages of about 1000 m y have been found in Ontario, along the Appalachians from New York to North Carolina, and also beneath the sedimentary covering in Michigan, Ohio, and West Virginia. Measurements have been made on muscovite, biotite, microcline, uraninite, and zircon. This occurrence is interpreted as indicating the extent of igneous intrusion and metamorphism accompanying a major orogeny about 1000 million years ago.