John Walter Gregory, a British geologist and explorer with wide interests, became a wool sales clerk at the age of 15 but continued his education by attending night classes in natural science, matriculating in 1886. From 1887 to 1900 he was an assistant in the Department of Geology of the British Museum (Natural History) under Robert Etheridge senior. Through further study at Birbeck College (University of London) he obtained the degrees Bachelor of Science (BSc, 1891) and Doctor of Science (DSc, 1893), the latter for his studies of fossil polyzoa, corals and echinoids. During his period at the British Museum he travelled widely. In 1891 he visited North America and in 1892-1893 undertook an expedition to British East Africa (now Kenya, Uganda and Tanzania). He was the first scientist to reach the glaciers on Mount Kenya, and the first to recognise the significance of the Rift Valley and offer a theory of its formation. He published his observations in a book, The Great Rift Valley; being a narrative of a journey to Mount Kenya and Lake Baringo, with some account of the geology, natural history, anthropology, and future prospects of British East Africa (London 1896). In 1896 he participated in the first crossing of the island Spitsbergen, and in 1899 travelled to the West Indies. He was a prolific writer, publishing papers on the geology of, among other regions, British East Africa (1894, 1900), the West Indies (1895) and Somalia (1896). One of his specific interests during this period was fossil Echinoidea, resulting in descriptions of specimens from Australia (1890, 1892), Barbados (1892), and Egypt (1898). He also compiled A catalogue of the fossil Bryozoa (Polyzoa) in the Department of Geology, British Museum (Nat. Hist.) (1899-1922).
From 1900 to 1904 Gregory was professor of geology at the University of Melbourne and (from 1901) also director of the Geological Survey of Victoria. His work during this period resulted in several books, including The climate of Australia (1904); Australia and New Zealand (2nd ed. 1907), in which he described these countries and his travels in them; The geography of New Zealand (1905); and The dead heart of Australia (1906), in which he described a journey around Lake Eyre, South Australia, during 1901-1902. He was elected a Fellow of the Royal Society of London in 1901, and was also a Fellow of the Geological Society of London. In 1904 he accepted a post as professor of geology at the University of Glasgow, where he remained to his retirement in 1929. During his career he produced over 200 publications in geology and palaeontology.
In 1905 Gregory came to South Africa to attend the joint meeting of the British and South African Associations for the Advancement of Science, having been a member of the former since 1894. On 29 August 1905, in Johannesburg, he read two papers before the associations. The first dealt with "The banket of Southern Rhodesia". It was included in the Addresses and papers... published after the meeting (1905, Vol. 2, pp. 101-109) and in more detail in the Transactions of the Institution of Mining and Metallurgy (London, 1905-1906, Vol. 15, pp. 563-578). Having visited that country recently he was able to ascertain that most of the strata in Mashonaland (Zimbabwe) to which the name "banket" had been applied were conglomerates of fluviatile origin and differed in some respects from the conglomerates of the Witwatersrand. His second paper dealt with the formation of gold pockets in the Ballarat Goldfields of Australia.
After his return to Britain Gregory published two papers on the origin of the gold in the Witwatersrand goldfields, the first in the Transactions of the Institution of Mining and Metallurgy (1908, Vol. 17, pp. 2-41) and the second, a supporting statement, in Economic Geology (1909, Vol. 4, pp. 118-129). He regarded the gold-bearing deposits as beach accumulations on a tide-swept shore, with channels cut through the material by streams and tide races, and compared the rich sheets of banket with the black iron-sand beaches of New Zealand. He also put forward the thought that the Witwatersrand beds were of Precambrian age and thus not as young as many early investigators had assumed. More than 20 years later he restated his conclusions in "Professor Graton on the Rand banket" (Transactions of the Geological Society of South Africa, 1931, Annexure to Vol. 34, pp. 23-36).
Gregory's other publications on the geology of sub-Saharan Africa included papers on the palaeozoic glaciations of Australia and South Africa (Report of the British Association..., 1906), the geology of Benguella (Transactions of the Royal Society of Edinburgh, 1916), Cretaceous Echinoidea from the neighbourhood of Lobito Bay (Ibid, 1916), further papers and a book on the geology of the Rift Valley and East Africa, which he visited again in 1919 (1919-1930), and "The ancient river system of the Kalahari and the possibility of its renewal" (Nature, 1924). He was a member of the committee appointed by the British Association to investigate the correlation and age of South African strata and on the question of a uniform stratigraphical nomenclature, and submitted the committee's report to the association in 1910. In recognition of his outstanding contributions to geology the Geological Society of South Africa elected him an honorary life member in 1914.
Gregory further enhanced his reputation as a geological explorer by expeditions to remote regions. In 1912 he visited Angola and in 1922 undertook a 2500 km journey of foot from Burma to south-western China and Tibet, accompanied by his son. His other contributions to science included books such as Geography: structural, physical and comparative (1908), which was particularly influential; Geology (1910); The elements of economic geology (1927); a treatise on the geology of Tibet (1923); and numerous papers on the geological and geographical observations made during his world-wide expeditions. He was also interested in anthropology, and was one of the authors of a popular book by H.N. Hutchinson and others on The living races of mankind (1901). Later in life he published a book on The menace of colour: a study of the difficulties due to the association of white and coloured races... (1925). He served as president of the Geological Society of London during 1928-1930. Remaining active to the end, he drowned on an expedition to Peru. Honorary degrees were conferred on him by the universities of Liverpool, Glasgow and Lima.