Summary: Mercury has been determined by radiochemical neutron-activation analysis in nineteen representative rocks from the Skaergaard intrusion and in the separated cumulus minerals of five. The chilled marginal gabbro contains 0·23 ppm Hg, values in the Layered Series rocks ranging from 0·07 to 0·34 ppm, in one exceptional case reaching 1·23 ppm Hg. There is a tendency for mercury to be more abundant in leucocratic than in average or melanocratic rocks at a similar horizon. Some- what higher levels of mercury are found in the granophyric rocks at the top of the intrusion.
Apart from a weak and sporadic tendency to be preferentially enriched in plagioclase, the distribution of mercury between the various cumulus phases is fairly uniform and it is thought to occur as uncharged atoms mainly occupying spaces resulting from lattice defects and imperfections rather than in specific structural sites.
The distribution pattern of mercury in the intrusion appears to be determined by its high volatility and chemical inertness; no real evidence of any chalcophile character is observed.