While the Highland work was still going on, in 1888 Peach and Horne resumed their work on the Southern Uplands. In 1878 and subsequent years, Lapworth had shown that the original survey of the Ordovician and Silurian was unsatisfatory. Peach and Horne began their revision with the Moffat sheet (16) and the Loch Doon sheet (8), which had been surveyed but not published.
These sheets were then issued in 1889 and 1893. Thereafter, at odd times during the autumn and spring seasons, when work was impossible on their Highland ground, they gradually extended their search and made exhaustive examination of most of the important field exposures, adding notes and lines to the original six-inch maps. Peach made himself an authority on the palaeontology, in particular the graptolites and identified them with precision and accuracy. He also drew up the cross-sections with which the great Memoir of 1899 is illustrated. Horne, meanwhile, wrote the text and the work on the petrology of the igneous rocks was done by Teall. Though produced under less than ideal conditions the Memoir stood for fifty years before any of its ideas were challenged: surely a great tribute to the men who produced it.