The third part of the debate about time classification and correlation of Precambrian rocks and events in Canada continues with discussion of the fundamental philosophies of geological time scales, assessment of previous proposals and the description of a chart with three scales. This chart, intended for use in the Geological Atlas of Canada, includes a chronometric scale for international correlation and reference to isotopic ages, the chronometric/chronolithic hybrid scale proposed for the Decade of North American Geology publications, and a modified (primarily chronolithic) version of Stockwell's chrono-orogenic scale which appeared in the first part of this debate.