Arthur Lewis Hall, geologist, was the son of William Hall, a clergyman of the Church of England, and his wife Mary Ann Smith. He spent his youth in Germany, attending schools in Freiburg, Bonn, Schwehn (Westphalia), and Cassel. Returning to England in about 1891 he obtained a studentship at the University College of Bristol. He matriculated and passed the intermediate examination of the University of London, and in January 1896 continued his studies at Gonville and Caius College, Cambridge. There he graduated as Bachelor of Arts (BA) in June 1899, with first-class in both parts of the natural sciences tripos, and received the University Harkness Scholarship in geology. That same summer he received training in geological surveying when he accompanied Mr Phillip Lake of St Jonh's College, Cambridge. to Wales. In April 1900 he became a teacher at Dulwich College, near London, but also continued his study of the geology of Britain, Ireland, and the Alps. In August 1900 he married Rosalie Powell of Bristol, with whom he had at least three sons and a daughter. Late in 1902 he resigned his post to take up an appointment as geologist to the Geological Survey of the Transvaal Colony, established after the conclusion of the Anglo-Boer War (1899-1902) under the directorship of H. Kynaston*. He was awarded the Masters and Doctoral degrees of the University of Cambridge while in this country.
Hall arrived in Pretoria in January 1903 and commenced surveying the geology in the neighbourhood of Pretoria. For a few years he worked in an ever widening area to the east, north and west of the city, reporting his results in the Annual Reports of the survey, with those of his colleagues Kynaston, E.T. Mellor* and, from 1906, W.A. Humphrey*. Field work was carried out under difficult circumstances and with meager facilities, and no accurate base maps were available on which to plot the results. Yet during his first eight years Hall surveyed some 40 000 square kilometers of country and travelled almost 30 000 kilometers, mostly on foot. He was a good observer, both in the field and through the microscope, and a fluent writer. His geological maps have sometimes been critisized for lacking detail, but they should be judged as the result of exploratory, rather than detailed, surveys. After the Transvaal Colony became part of the Union of South Africa in 1910 Hall continued his work in the Geological Survey of the Union until his retirement in January 1932. He was appointed assistant director of the Survey from the first of January 1917, but appears to have already been acting in this position for about a year.
In addition to geological mapping Hall investigated the mineralisation of the rocks that he encountered, particularly the possible economic exploitation of mineral deposits associated with the Bushveld Igneous Complex. Among others he reported on the tin-fields of the bushveld (1905), magnesite deposits at Malelane in the Lowveld (1907), the goldfields at Haenertsburg (1907) and Pilgrim's Rest (1910), and the tin deposits of Mbabane in Swaziland (1913). The increased demand for resources during World War I (1914-1918) resulted in a more rapid assessment of South Africa's mineral deposits, in which Hall participated. For example, he produced memoirs on Asbestos in the Union of South Africa (1918), Mica in the eastern Transvaal (1920), Corundum in the northern and eastern Transvaal (1920), and Mineral resources of South Africa (1924).
However, his most important contributions were his stratigraphic and petrologic studies, which were published in the form of several memoirs. The first of these dealt with The geology of the Murchison Range and district (1912). Next he described The geology of the Barberton gold mining district, including the adjoining portion of northern Swaziland (1918, 324p). This was an outstanding example of the single-handed study of a region with a complex geological structure that was previously virtually unknown. Using the name Swaziland System for the strata older than the basement granite, he subdivided it into a basal Onverwacht Series of lavas and tuffs, a middle Moodies Series of slates, greywackes, conglomerates, banded ironstones, and quartzites, and an upper Jamestown Series of basic schists with serpentine and other basic rocks. In 1922 he acted as guide to the Shaler Memorial Expedition, which came to South Africa with the principle object of studying the Bushveld Igneous Complex. For six weeks he conducted its members (three American experts plus G.A.F. Molengraaff*) through Sekukuniland, where the geological problems of the complex could best be studied. In 1929 he was the secretary-general of the 15th International Geological Congress, which was held in Pretoria, and led its delegates on a similar excursion. For this occasion he compiled a guide to the excursion entitled The Bushveld Igneous Complex, with special reference to the Eastern Transvaal (1929, 83p), followed later by an outstanding and more comprehensive memoir on The Bushveld Igneous Complex of the central Transvaal (1932, 554p). He and G.A.F. Molengraaff furthermore wrote a monograph on the geological history of The Vredefort mountain land in the southern Transvaal and the northern Orange Free State (Amsterdam, 1925, 183p). These publications gave him a world-wide reputation and made him one of South Africa's great earth scientists.
From August 1916 until his retirement in 1932 Hall's duties as assistant director of the Geological Survey of the Union included responsibility for the museum of the Geological Survey, then still part of the Transvaal Museum. With his characteristic enthusiasm he re-designed the displays, including an attractive and representative collection illustrative of the geological history of South Africa. The museum was opened to the public on 1 November 1920. He also provided large numbers of labelled rock specimens to the South African Museum in Cape Town and was honorary curator of its geological and mineralogical collections from 1918 to 1929. During this time he compiled the first of his invaluable bibliographies of South African geology, containing references to over 5700 sources published before the end of 1920, arranged alphabetically by author (Hall, 1922). A subject index to this volume appeared a few years later. The bibliography was later extended in three further publications to cover the period 1921-1935.
After his retirement Hall continued work as a consulting geologist and wrote several further publications. One of these was a comprehensive work, Analyses of rocks, minerals, ores, coal, soils and waters from southern Africa, published as Memoir 32 of the Geological Survey (868p) in 1938. It tabulates over 5000 chemical analyses of located samples. All together he had more than 100 publications to his credit.
Hall was a member of the Geological Society of South Africa from 1903, served on its council from 1910 to 1940, and as its president for 1913/4. In 1932 he was awarded the society's first David Draper Memorial Medal. He became a member of the South African Philosophical Society in 1905 and was elected a Fellow of its successor, the Royal Society of South Africa, in 1909. For some years he was a member of the South African Association for the Advancement of Science. In 1925 he was president of the South African Geographical Society. His presidential address, on "The Transvaal Drakensberg", was published in the South African Geographical Journal that same year. The University of Cambridge awarded him an honorary Doctor of Science (Sc D) degree and he was elected a Fellow of the Royal Society of London and of the Geological Society of London (1900). The latter society awarded him its Murchison Medal in 1930. He became a corresponding member of the Geological Society of America in 1934 and was a member of the Society of Economic Geologists.
Hall had a robust physique, a forthright character and a somewhat gruff manner, but was a kind and gentle person among his friends. He played an active role in the Public Servants' Association and was largely responsible for persuading the professional and technical staff of the public service to join the association, rather than forming themselves into a separate body. Music was another of his long-term interests and he often played the violin in private performances of orchestral works and chamber music.