The British Geological Survey (BGS) petrology collections contain almost 1500 Scottish rock samples (with thin sections) deposited by Archibald Geikie, including BGSS1, an analcime gabbro from Salisbury Crags, Edinburgh. High-quality thin section images are now available from the BGS’s Britrocks online database. The geospatial distribution of these samples is analysed. They reflect the development of geological mapping and igneous petrology in Scotland from the 1850s to the 1890s. Geikie had the opportunity to study Nicol’s original thin sections in 1851 and he met both Sorby and Zirkel, early pioneers of petrography. Lacking management support, he cut many of his own thin sections while mapping the Clyde Plateau lavas during the 1860s, leading to publications on Carboniferous and Tertiary volcanism. When appointed Director of the newly formed Geological Survey of Scotland in 1867, he was able to establish a petrological laboratory in Edinburgh. Time pressures resulting from his subsequent promotion to Director-General, and increasing quantities of metamorphic rocks, then necessitated the appointment of Hatch and Teall as petrographers for the Survey. Teall’s work was particularly important in the detailed petrography of the gneisses and mylonites associated with the Highlands Controversy.

Supplementary material: The rock samples deposited in the Survey collections by Archibald Geikie are listed on a spreadsheet, which will be updated when more slides are imaged or if URLs change. The spreadsheet is available at https://doi.org/10.6084/m9.figshare.c.4360664.