6. Summary: A series of rocks from the Skaergaard intrusion, East Greenland, has been analysed spectrographically for certain trace elements. One of the rocks analysed is the chilled, marginal gabbro considered to represent in composition the undifferentiated olivine-gabbro magma from which the varied rocks of the intrusion have developed. The amounts of the trace elements present in this rock (table I, column 1) show relatively good agreement with the best available comparison analyses of an average gabbro prepared by Noll (table I, column C), except in the case of SrO which is ten times as abundant as in the average. The acid gneiss which is the dominant rock surrounding the intrusion is also shown to be richer in SrO and BaO (table I, columns 10 and 11) than average granite (column D). It is tentatively suggested that the outer layers of the earth in this part of east Greenland contain an amount of strontium and barium which is above the average.
The majority of the rocks analysed for trace elements, which range from gabbro-picrite, through normal olivine-gabbro, ferrogabbro, basic hedenbergite-granophyre, to a normal acid granophyre (table I, columns 2–9), were produced by fractional crystallization from a fairly normal olivine-gabbro magma. In this series of rocks chromium and nickel tend to be concentrated in the earlier differentiates, vanadium and cobalt in the early middle differentiates, copper and lithium in the late middle differentiates, while molybdenum, zirconium, thorium, lanthanum, and rubidium are concentrated in the latest differentiate, the acid granophyre. Of the other elements for which the data are satisfactory, strontium occurs in considerable amount except in the first differentiate, the gabbro-picrite, and the last, the acid granophyre, while barium shows a continuous and marked increase in amount throughout the whole range of the differentiation series.
The probable location of the trace constituents in the various minerals of the rocks is briefly considered and in the case of certain of the elements the variation is shown to be related to ionic size and charge.