The oldest known occurrence in North America of an ophiolite, considered to be a piece of ancient ocean crust, has been reported in the Cape Smith Belt in northern Quebec, Canada. The recognition last summer of a key structural component of the characteristic ophiolite suite has buttressed confidence in the theory that the 1900‐Ma fragments of an ocean basin were accreted to an early Proterozoic Canadian continent. The tectonic mixing of oceanic and continental crust is strong evidence for the operation of plate tectonics early in Earth's history.