Inroduction. In early Carboniferous times an extensive area of volcanic activity stretched from the Solway Firth north-eastwards to the neighbourhood of Greenlaw and Duns. The igneous rocks to be described in the following pages are the eroded relics of the northern end of this volcanic belt. Because of post-Carboniferous folding, lava flows at the present day from a U-shaped outcrop separating older and younger sedimentary rocks at the south-west end of a synclinal trough. As the town of Kelso is situated within the syncline, these lavas have long been known as the ‶Kelso traps.″ Previous Geological Work. The igneous rocks of the Kelso district attracted a certain amount of attention in the early days of Scottish geology, but have on the whole been much neglected until recent years. One of the earliest accounts is that of David Milne, later known as David Milne-Home (1837).1 Milne’s paper was accompanied by a small-scale coloured geological map on which the limits of the Silurian, Upper Old Red Sandstone, and Carboniferous sediments are shown with some degree of accuracy. Most of the well-exposed igneous rocks are also indicated. James Nicol made a further contribution to our knowledge of the Kelso traps (1847). His coloured map shows in a general way the south-west end of the Kelso syncline, with a U-shaped outcrop of lavas enclosing Carboniferous sediments. Sir Archibald Geikie, in one of his early contributions to Scottish geology (1863, pp. 37, 47), described a few small outcrops of lava and tuff that occur in