The investigation of the olivines in the picrite, picrodolerite, and crinanite of the Garbh Eilean sill is part of a research program on the geochemistry and petrology of the rocks of the Shiant isles, situated 20 miles off the west coast of Scotland. Optical and chemical work on specimens from a section of the sill, extending from sea level up to 395 feet, shows that the olivines in the upper picrodolerite and the crinanite are zoned, the range of zoning and the iron content increasing with height.