The drainage pattern of the Canadian Shield is at least pre-Ordovician and its present destructional topography developed in pre-Paleozoic time. One or more of the features of localities in which details of the Ordovician-Precambrian surface have been described in the literature are generally diagnostic of a paleoplain now being exhumed. Data from the literature are summarized and an extensive review of the whole of the Canadian Shield is given. A bibliography is appended.