214 FAMOUS GEOLOGISTS/Murchison The position of Director-General of the Geological Survey of Great Britain fell vacant in 1855, upon the decease of its founder Sir Henry De la Beche, and Murchison was appointed in his place, though already in his sixties It proved to be an astute move, so far as the Survey’s progress was concerned, for Murchison had innumerable contacts and used them to advantage to build up the organization considerably He was indefatigably a man of organization, and competent, with his experience in the running of several societies and associations The appointment was gratifying to Murchison as it ensured that the official maps should be constructed and coloured according to his interpretation and subdivisions of Palaeozoic geology, to the extent that the Cambrian was almost driven off the map for British geology Much of Murchison’s geological work in his later years was focused on Scotland, where a separate branch of the Survey was established in 1867, though surveying had begun there back in 1854 Murchison’s Scottish work involved him in the last of his three great controversies, and involved the attempted expansion of Silurian colours over the greater part of northern Scotland There is today thought to be a great thrust-plane (the ‘Moine Thrust’) that runs from the north coast near Lochs Durness and Eriboll to the south-west, terminating in the southern part of Skye To the west, one finds ‘Fundamental [Lewisian] Gneiss’ (so called by Murchison), overlain unconformably by the unfossiliferous Torridonian Sandstone Lying unconformably on this there is a series of sediments, including a ‘quartz rock’ and the fossiliferous Durness Limestone Over this lies the complex unit called the Moine Schists, above the thrust plane and extending eastwards until it is itself overlain unconformably by Old Red Sandstone on the eastern side of the country But the structure near the thrust plane is complicated, with folding, inversions, and apparent duplication or repetitions of strata; in places the gneiss ‘reappears’, both near the thrust fault and again further east Murchison visited the north-west Highlands of Scotland in 1855 (with the Aberdeen University geologist James Nicol), in 1858 (with the local amateur naturalist Charles Peach), in 1859 (with the Survey officer Andrew Ramsay), and in 1860 (with the young surveyor Archibald Geikie) Fossils regarded by Murchison as Lower Silurian were found by Peach in the Durness Limestone (at a lower horizon than the thrust plane) All the strata appeared to dip gently to the southeast, with a strike approximately parallel with what is now thought to be the thrust-fault system The outcome of all this work was that in the view of Murchison (and also Ramsay and Geikie) there was an essentially simple ascending sequence (with unconformities) from ‘Fundamental Gneiss’ on the west (regarded as lying at the bottom of the whole stratigraphic column for Britain) through to the Old Red Sandstone on the east, with a repetition of quartz rock into distinct upper and lower units, and also repetition of the gneiss This meant that the Moine Schists, lying between the supposed Lower Silurian Durness Limestone and the Devonian Old Red Sandstone, though unfossiliferous, could be regarded as Silurian So when a geological map of Scotland was published by Murchison and Geikie in 1861, large areas of northern Scotland were represented in Silurian colours Murchison’s empire was again expanding in a manner that he found most satisfactory As to the Cambrian, Murchison allocated the unfossiliferous Torridonian Sandstone to that System, so Sedgwick saw some expansion his empire, but not by rocks with well-characterized fossils But Nicol’s reading of the structure was very different from Murchison’s He came to the view that there was repetition of the western and eastern metamorphic rocks due to a large (high-angle) fault, and that the resultant fissure had been filled in part by some kind of igneous rock (He was perhaps mistaking some gneiss for igneous rock.) If this interpretation were correct then placement of the Moine Schists in the Silurian would be suspect So Nicol and Murchison fell out, and Nicol thereafter conducted his work separately from the Survey chief The issues were debated at the British Association meeting in Aberdeen in 1859, where both geologists put forward their cases From his stronger social position, Murchison was judged the winner by most geologists, and in fact Nicol’s idea was by no means wholly correct The results of this encounter were most satisfactory to Murchison and Geikie, who became his mentor’s advocate and eventually his sympathetic biographer Murchison got more Silurian colour onto the geological map of Britain In time, Geikie was appointed head of the Scottish branch of the Survey, and, when Murchison endowed a chair in geology at Edinburgh University (with Geikie’s urging), it was Geikie who moved smoothly into the position, holding it concurrently with his post in the Survey Later he became Director-General of the Survey, President of the Royal Society, and one of Britain’s leading geologists However, the Murchison theory of the structure of the north-west Highlands was shown to be in error by Charles Callaway’s and Charles Lapworth’s mapwork in the early 1880s, and the reputation of the deceased Nicol was restored Lapworth showed that the structure involved folding and thrust-faulting (a