The validity of the Archaic stage in general and of the Northern Archaic Tradition in particular are examined as they apply to the Mackenzie River valley in the western Canadian Subarctic. Archaeological data from five Middle Prehistoric complexes are presented along with palaeoenvironmental information, all of which tend to undermine the suggestion of a movement of Archaic people from the northern Plains during the Hypsithermal. Instead, we seem to be looking at the diffusion of a few isolated traits into a long-established boreal forest ecosystem. The Mummy Cave complex on the northern Plains is identified as the probable immediate source of, particularly, side-notched points, which at about this time achieved a continent-wide distribution.