In his Great Ice Age Professor James Geikie1 described a section of gravels and gutta-percha clays which was exposed at the west end of Neidpath Tunnel when excavations were being made. No sections of these deposits have been available for a long time, but fortunately one was re-exposed by a landslip which occurred in the south bank of the railway cutting at the west entrance to Neidpath Tunnel, after heavy rain, in the spring of 1925. The landslip was 80 feet wide and disclosed a vertical section of about 35 feet of horizontally bedded gravels, sands, and clays. The section lay between the 600- and 700-foot contours, and the lowest bed exposed was about 50 feet above the level of the River Tweed, which enters the Neidpath gorge 60 yards to the north-west. Beneath several feet of slipped angular rock-debris the following section was measured:— The deposits are similar to those described by Geikie, and from their character and flat-bedding are clearly of lacustrine origin. The alternating character of the beds suggests a rhythmic seasonal deposition of sediment. The laminated bands of gutta-percha clay are tough and compact silts, probably accumulations of fine sediment during winter months. The associated thicker sands and clayey bands represent coarser material borne into the lake by melt-waters during summer months. The gutta-percha clays are mainly in the lower part of the section. They are absent from the coarser deposits at the top and are present only as thin partings in the middle. The passage