SOME prominence has been given recently to the results and implications of isotope age studies1–4 in the early Precambrian rocks of the Godthab region, southern West Greenland. The studies were initiated after field investigations5 suggested that the Godthabsfjord region may contain outcrops of the oldest rocks in the earth's crust. McGregor5 has grouped these rocks into an older and a younger set of gneisses (respectively the Amitsoq and Nuk gneisses) separated in time by dykes (the Ameralik dykes), metavolcanic and metasedimentary rocks (the Malene supracrustals) and stratiform meta-anorthosites. Among conclusions drawn from the isotope work is that based on initial ratios of 87Sr/86Sr that the parents of the Nuk gneisses in the Godthabsfjord area cannot have been derived by partial or complete melting of the older Amitsoq gneisses3. We wish to comment on the applicability of this conclusion to the Nuk gneisses mapped in the area immediately to the south.