Lapworth, at the time of his 1878 paper on the Moffat Series, was the world's foremost expert on graptolites, and in that paper he gave the first great demonstration of the biostratigraphical value of graptolites. Peach & Home's resurvey of the Southern Uplands of Scotland extended Lapworth's ideas and his use of graptolites across the entire region. Peach's graptolitic work for the Survey is discussed: even though he identified a smaller repertoire of graptolites than Lapworth had, and often identified their general horizons rather than exact zone, his results are considered broadly correct. His faunal lists often emphasise the oldest faunas from the Moffat Shale inliers, presumably in order to stress their supposedly anticlinal structure. Subsequent work has seen a great extension of graptolite taxonomy and provided more detailed biostratigraphical subdivision, especially in the Silurian. The model of the Southern Uplands as an imbricate thrust stack is constrained by identifying the youngest (rather than oldest) fauna from the Moffat Shale inliers or, where possible, graptolites from the overlying greywacke formations. Such work has enabled the identification of about 25 thrust tracts in SW Scotland and of out-of-sequence thrusting in the Moniaive and Peebles areas to the NE.