SummaryAn account is given of one of the most heated controversies in nineteenth-century British geology—the battle between Archibald Geikie and John Judd concerning the interpretation of the Palaeogene igneous rocks of the Inner Hebrides, particularly those of the Cuillins and the Red Hills of Skye. The controversy erupted in the first instance over the question of the respective ‘territories’ of the two geologists, then developed into disagreement as to the origin of the plateau lavas of Skye: were they formed from (...) fissure eruptions (Geikie's view) or from the outpourings of great volcanoes (Judd's view)? Debate then focused on the question of the relative age of the gabbro of the Cuillins and the granite (granophyre) of the Red Hills. A certain locality at Druim Hain (Druim an Eihdne) at the junction between the two rock-types became crucial for the dispute. Following earlier observers, Judd held that the granite was older and had been intruded by the gabbro. Geikie took the opposite view. Geikie's work relied particularly on field observations, for which he was assisted by several other geologists. Judd, who worked by himself, rested his argument more on the evidence furnished by petrology, using thin sections. Both geologists were influenced by Ferdinand von Richthofen. Geikie's work appeared to be vindicated in his own lifetime by the map work of Alfred Harker, which effectively closed the controversy. But later commentators such as Walker hold that in a sense both were correct. There were indeed great volcanoes active in the Inner Hebrides in the Palaeogene, as well as fissure eruptions. Moreover, recent mapping does not support all the observations of Geikie and Harker. The controversy illustrates different styles in nineteenth-century geology, with petrological arguments, based on the examination of thin sections, pitted against field observations. It may also be seen as being linked with the ongoing rivalry in the nineteenth century between the members of the Geological Survey (particularly the Directors General) and the ‘amateur’ university geologists. Geikie prevailed in the debate in part because he was able to draw on more resources for its prosecution, being helped by various friends and members of the Geological Survey. The study draws on the newly discovered Geikie archive at Haslemere, which contains his complete outgoing official correspondence, and 27 of his field notebooks, previously missing. With the help of this material, it is possible to gain a clearer insight into the methods deployed by Geikie in his fieldwork, and his ways of working and thinking. (shrink)