(b.Guernsey, Channel Islands, 6 October 1773; d. Poltair, Cornwall, England, 20 August 1835)
Macculloch was descended from a Scottish family, the Maccullochs of Ardwell, Galloway. His father, James Macculloch, after being engaged in business in Brittany, retired to Cornwall, where Macculloch attended school. He entered Edinburgh University to study medicine and graduated M.D. in 1793. His interest in geology arose during his stay in Edinburgh, possibly because he attended the lectures of John Walker, professor of natural history, who included geology and mineralogy in his course.
Macculloch’s first appointment was as assistant surgeon to the Royal Regiment of Artillery, a branch of the army controlled by the Master General and Board of Ordnance. In 1803 he was appointed chemist to the Board of Ordnance, From 1807 he also practiced at Blackheath, near London. He became a member of the newly formed Geological Society of London in 1808, and its president in 1816.
In 1811 he gave up his medical practice and thereafter was employed by the Board of Ordnance in tasks requiring a knowledge of geology. He spent the summers of 1811 to 1813 in Scotland, investigating what rocks could be used safely in mills for grinding gunpowder. In 1814 the Board of Ordnance appointed him geologist to the Trigonometrical Survey then being carried out in Scotland. This involved two tasks. One was to choose sites geologically suitable for setting up the zenith sector used to determine the meridians; the other was to select a mountain geologically suitable for determining the earth’s density (a previous determination made by the astronomer Maskelyne had in 1774 proved unsatisfactory for geological reasons).
While engaged in this work Macculloch used his spare time to record additional geological information with the intention of constructing ultimately a geological map of the whole of Scotland; and he tried to persuade his employers that official support for the preparation of such a map would be in the national interest. His employment in Scotland was terminated in 1820. During this period Macculloch also lectured in chemistry during the winter at the Royal Military Academy at Woolwich and later held a similar post at the East India Company’s College at Addiscombe, where he also taught geology. He was elected a fellow of the Royal Society in 1820.
In the next few years Macculloch spent some time in completing for the Board of Ordnance reports on the work he had carried out in Scotland. In 1826 his post as chemist was abolished. He was then informed that for the purpose of completing a geological map of Scotland he could transfer his services to the Treasury, which would pay him a salary and expenses.
From 1826 until about 1832 Macculloch visited Scotland every summer to complete his geological survey. The question of whether his geological map should be published caused some delay, but eventually the Treasury sanctioned publication. Macculloch died as a result of a carriage accident in 1835; the map was published, posthumously, in 1836. He married a Miss White in 1835.
Macculloch was the author of a large number of books and papers of geological, mineralogical, and chemical interest. His most important work was that carried out in Scotland. Here his knowledge of mineralogy and chemistry proved invaluable in studying the igneous and metamorphic rocks, which occur over about three-quarters of the country. He was an acute observer of geological phenomena, and the value of his published work was often enhanced by his careful sketches of the field relations between the different types of rock.
In some respects Macculloch was conservative in outlook. He was unwilling to accept new geological ideas unless supported by evidence acceptable to him. He examined the lithological and mineralogical characteristics of the sediments carefully, and accepted that their contained fossils yielded information about the physical conditions existing at the time they were formed. He believed, however, that contemporaneous knowledge of fossil forms and their distribution was inadequate. He felt that their use as stratigraphical indexes and for correlation was unreliable and likely to cause confusion, even though by about 1820 they were quite widely used for this purpose. Contemptuous of stratigraphical paleontologists, Macculloch once described them as “namby pamby cockleologists and formation men.” Nevertheless, in A Description of the Western Isles of Scotland (1819), he recorded the occurrence of Jurassic fossils in the islands of Skye and Raasay, and remarked on their similarity to those found in Jurassic rocks in Somerset and Gloucestershire in England.
Macculloch also found for the first time organic remains (Serpulites macculhchii) in the Cambrian quartzite in the northwest highlands of Scotland. Though he did not recognize the significance of this discovery, it later proved of great importance in working out the complicated overthrust rock succession in this area.
His Description of the Western Isles of Scotland was Macculloch’s most important book. The numerous islands described, large and small, many of which had not previously been examined by geologists, contain rocks ranging in age from Precambrian to Tertiary, including many igneous rocks. His descriptions of the igneous rocks and the sketches and maps in the accompanying atlas promoted a true understanding of the nature and origin of igneous rocks at a time when the mistaken views of Werner on their origin had not yet been eradicated.
Macculloch’s Geological Classification of Rocks … Comprising the Elements of Geology (London, 1821) describes his system of classifying rocks. He divided rocks into two main classes: Primary and Secondary. He subdivided Primary into unstratified (granite) and stratified (mainly gneisses and schists, with some sediments). The secondary included all the younger sediments and a few “unstratified” rocks, which his descriptions clearly indicate were igneous intrusions, although he did not specify them as such. Macculloch also described in detail the occurrences of basalt lava (“trap”), the remains of the extensive Tertiary basalt lava plateau off the west of Scotland. Although he realized they were analogous in appearance and composition to recent lava flows, he seemed unwilling to commit himself to the view that the “trap” rocks were true lava flows. He regarded the problem as an obscure one.
MaccuIloch’s rock classification was based on that of Werner—as a matter of convenience because it was still widely used—but this classification did not imply acceptance of Werner’s ideas about the origin of rocks. He omitted Werner’s “transition” group, regarding it as an unjustifiable complication.
Macculloch’s last geological book was his System of Geology,With a Theory of the Earth (London, 1831). His “theory of the earth” was largely Huttonian in concept, modified by the suggestion—perhaps derived from Cuvier—that a succession of revolutions might have brought about the extinction of some forms of life. An unusual feature of the work is the inclusion, in an appendix, of advice on the qualifications required of a geologist; on describing geological observations; on the instruments required; and on constructing geological maps. Much of this information is still useful.
Macculloch’s geological map of Scotland, on a scale of four miles to the inch, was the first large-scale geological map of the country. It differentiated eighteen rock types and was largely, if not entirely, based on his own observations. It was a remarkable achievement for one man, especially considering the difficulties of access to the remoter parts of the country and the inaccuracies of the only topographical map available. Though gradually superseded by other maps during the nineteenth century, some of the areas he described had still not received detailed examination even as late as the mid-twentieth century.
Macculloch’s observations greatly advanced general knowledge of the varied rock formations in Scotland, especially that of the igneous rocks. Though his work is now largely forgotten, it was appreciated in his time by Lyell, who made several references to it in both his Principles of Geology and his Elements of Geology. In an obituary notice, Lyell recorded “that as an original observer Macculloch yields to no other geologist of our time, and he is perhaps unrivalled in the wide range of subjects on which he displayed great talent and profound knowledge,” and he added that he had “received more instruction from his labours in geology than from those of any living writer.”
I. Original Works. Macculloch’s geological works include A Description of the Western Isles of Scotland … Comprising an Account of Their Geological Structure, 3vols., with an atlas of plates and maps in one vol. (London, 1819); A Geological Classification of Rocks… Comprising the Elements of Geology (London, 1821); A System of Geology, With a Theory of the Earth, 2 vols. (London, 1831); A Geological Map of Scotland by Dr.Macculloch, F.R.S. &c., published by order of the Lords of the Treasury by S. Arrowsmith (London, 1836). There are four different issues of the map, with different titles, dates, and publishers. The geology is the same in all issues. None is dated 1836, but independent evidence establishes this as the date on which the map was first published. Memoirs to His Majesty’s Treasury Respecting a Geological Survey of Scotland (London, 1836), published posthumously, accompanied the geological map.
A complete list of Macculloch’s scientific papers is in the Royal Society Catalogue of Scientific Papers (1800-1863), IV (1870), 153-155. Of the total of seventy-nine, forty-six are of geological or mineralogical interest. The earlier (1811-1824) are in the Transactions of the Geological Society of London; later papers (1819-1830) are mainly in the Quarterly Journal of Literature, Science and the Arts. Macculloch published several books on subjects other than geology which are listed in the usual reference works.
II. Secondary Literature. There is an obituary notice by Lyell in Proceedings of the Geological Society, 2 (1838), 358–359; sec also T. G. Bonney, Dictionary of National Biography, XII, 461-463; V. A. Eyles, “John Macculloch, F.R.S., and His Geological Map-FP an Account of the First Geological Survey of Scotland,” in Annals of Science, 2 (1937), 114-129; and “Macculloch’s Geological Map of Scotland: an Additional Note,” ibid.,4 (1939), 107.
V. A. Eyles
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