Jules Garnier, a Frenchman, appears to have been an engineer, for in 1884 he produced a publication on the elevated railroads of Paris. Earlier he had visited Oceania and New Caledonia (a French possession in the south-western Pacific Ocean) and published an account of these travels in 1871. His interests and expertise included geology, mining, mineralogy and metallurgy. For example, he wrote papers on the geology of New Caledonia, Tahiti and Oceania (1866-1873), as well as on the metallurgy of iron (1874). In 1891 he undertook a trip to North America where he concluded that the native copper of Lake Superior had been precipitated from a solution of copper sulphate by the action of decomposed organic matter and carried down by a river to be deposited as a copper-bearing conglomerate. A subsequent trip to Canada served to extend his views on the precipitation of metals and the formation of mineral deposits. In 1898 he also visited Australia, accompanied by his son, Pascal Garnier*. Their report dealing with mines and mining on that continent was published in France in 1900. In other publications he described the fjords of Norway, the dunes of the Sahara, Canadian nickel and platinum mines, and the uses of electricity in chemistry and metallurgy.
In 1895 Jules Garnier and his son came to South Africa and that year Jules published a preliminary paper on the gold deposits of the Witwatersrand in France. After also studying the diamond deposits around Kimberley he published a further extensive paper in the Mémoires de la Société des ingénieurs civils de France in March 1896. This paper was translated into English in Johannesburg under the title "Gold and diamonds in the Transvaal and the Cape", read before the Geological Society of South Africa in August and September that year, and published (under Jules's name only) in its Transactions (Vol. 2, pp. 91-103, 109-120; discussion pp. 124-127). Garnier described the thin carbon layers which his son had found associated with some gold-bearing reefs on the East and Central Rand and at Klerksdorp. He speculated that the carbon constituted the remains of organisms whose decomposition had created suitable chemical conditions for the precipitation of the gold in the form of trichloride. It was tentatively accepted at the time that the gold-bearing conglomerate was a beach deposit, and Garnier first suggested that the ancient beaches had formed along a closed sea, surrounded by high mountains on the northern side from which streams converged towards the basin.
Whereas his ideas on the origin of the Witwatersrand gold were considered informative, his view that the diamondiferous rocks at Kimberley had been upheaved in a plastic state by natural pressures, rather that by vulcanic action, was considered by H.S. Harger* to be inconsistent with well-established observations and was generally rejected. None the less Garnier's status as a scientist was such that he was elected an honorary member of the Geological Society of South Africa. He retained an interest in South African affairs, for in 1900 he published a book in London, England's enemies: a warning, which was a pro-British analysis of the causes and events leading up to the Anglo-Boer War. The mineral garnierite, a bright-green nickeliferous silicate of magnesium, was named after him.