T.G. Bonney was a British geologist who never visited southern Africa, but published some work locally. He showed an interest in fossils and geology from an early age and studied at St. John's College, Cambridge, from about 1852, graduating in classics and mathematics in 1856. After some time as a mathematics teacher at Westminster School he prepared for holy orders and was ordained a priest in 1858. He was elected a fellow of St. John's College the next year. From 1868 he was a tutor (and from 1869 a lecturer) in geology at that college and did much to promote the study of microscopic petrography. At some stage he was awarded the Doctor of Science (DSc) degree by the University of Cambridge. He was self-taught in geology, but in 1877 was appointed professor of geology at University College, London (concurrently with his post at St John's College) where he remained until 1901. He left Cambridge for Hampstead in 1881, but returned in 1905
Most of Bonney's work related to mineralogy, petrology and later glaciology. He knew the Alps well and was a good climber. A prolific writer, he published on the geology of various regions in Britain and continental Europe, on volcanoes, the Alps and the Canadian rockies. His introductory and more popular books included The story of our planet (1893), Ice-work (1896), Volcanoes (1899), Charles Lyell and modern geology (1905), and The building of the Alps (1913). He also wrote several books on the cathedral churches of England and Wales and on the holy places of Jerusalem. A number of his sermons were also published.
Bonney had a strong interest in the diamond-bearing rocks of Kimberley and some other South African mines. In 1891 and 1895, in collaboration with Miss Catherine A. Raisin, he published two papers in the Geological Magazine on the diamond-bearing rocks of Kimberley, followed by a further paper by him alone in 1897. Two years later, in a paper on "The parent rock of the diamond in South Africa" (Proceedings of the Royal Society, 1899, 1900) he concluded that diamonds had not originally been formed in kimberlite (the so-called blue ground), but rather in the coarse-grained, ultramafic rock known as eclogite. In response F. Garner Williams* examined some twenty tons of eclogite, which had been discarded as waste at the Kimberley mine, but found no diamonds in it. One of Bonney's subsequent papers, "On the supposed Kimberlite magma and eclogite concretions", appeared in the Transactions of the Geological Society of South Africa in 1905 (Vol. 10, pp. 95-100). His last paper on the diamondiferous rocks of Kimberley was published in Nature in 1908. He also edited a volume, Papers and notes on the genesis and matrix of the diamond (1897), representing the formerly unpublished work of Henry C. Lewis. In 1905 he was elected an honorary member of the Geological Society of South Africa.
Bonney was a member of the British Association for the Advancement of Science from 1871, serving as secretary in 1881-1885, president of Section C in 1886, a member of its Committee on Seismology around 1905, and as president of the Association in 1910. He was a Fellow of the Geological Society of London, of which he was secretary from 1878 to 1885, receiving its Wollaston medal in 1889. He was elected a Fellow of the Royal Society of London in 1878, and served as president of the Mineralogical Society during 1884-1886. Honorary doctoral degrees were conferred upon him by the Universities of Dublin, Sheffield, and Montreal. His autobiography, Memory of a long life appeared in 1921. His valuable collection of rocks and micro-sections was presented to the Sedgwick Museum, Cambridge, where he worked as a voluntary demonstrator after his retirement.