Two approaches to the time‐stratigraphic subdivision of the Australian Pre‐cambrian are possible. In one, bodies of rock are referred, by means of radio‐metric dates, to periods defined by chosen points on the absolute time‐scale. In the second, the boundaries of time‐rock units are defined at selected reference points on the ground, and these reference points are dated as accurately as possible by radiometric means. Geographically distant bodies of rock are correlated with “type” time‐rock units by radiometric dates.