I wish to correct by 40 feet the position hitherto assigned to the outcrop of the Ballachulish Slide (or Lag as it is safe to call it) in one of its four easily accessible exposures on the shores of Loch Leven. The change does not appreciably affect the mapping as shown on Sheet 53 of the Geological Survey one-inch-to-the-mile map of Scotland, but it is of some importance on the ground. The locality lies on the north shore of Loch Leven, within a few yards of the main road, opposite a small cottage, midway between Callert House and Callert Cottage. A conspicuous little summerhouse is built on the eastern edge of the quartzite listed below. The dip of all the formations is very steep, so that the breadths of outcrop, measured at right angles to strike, correspond roughly with thicknesses. Details are as follows:—