"A biotite-teschenite and a lugarite differentiate have been analysed spectrographically for trace elements.The rocks occur as part of a composite sill of Permo-Carboniferous age at Saltcoats, Ayshire.... The amounts of the trace elements present in the differentiated rock show in some cases very marked differences from those in the parent rock. Chromium and scandium in particular, diminish greatly during differentiation, while lithium and rubidium demonstrate the reverse process. The results have been correlated with the findings of Goldschmidt on the conditions governing the disposition of trace elements in crystallizing rock magmas." Complete chemical analyses are given.