The bicentenary of Georg Hartung, a German pioneer geologist and explorer

Abstract. We present a tribute to Georg Friedrich Karl Hartung (1821–1891), a less-known non-academic German geologist, on his 200th anniversary. Influenced by eminent 19th century scientific personalities such as Oswald Heer, Charles Lyell, and Alexander von Humboldt, he performed pioneer geological observations and sampling in the Azores, Madeira, and Canaries volcanic archipelagos. Later in his life he travelled to the USA and explored the Scandinavian countries. His scientific endeavours were published in several books and papers, many of them co-authored by academic German geologists and palaeontologists. His works on the macaronesian islands are deemed as classics, many enriched by his own detailed geological illustrations.


In the winter of 1850/51, suffering from catarrh, Hartung travelled to Madeira Island (Portugal) to seek a milder climate to ameliorate his poor health condition (Pinto and Bouheiry, 2007). In Funchal, he met the Swiss palaeobotanist Oswald Heer (1809Heer ( -1883, who travelled to Madeira due similar health reasons (e.g. Schröter and Heer, 1885;Bouheiry, 2013). During 35 this stay, Hartung accompanied Heer fieldwork (Heer, 1857;Schröter and Heer, 1885). Heer influenced him to start studying the geology of Madeira Island (Bouheiry, 2013). Hartung returned to Madeira Island in the following winter (1851/52), also traveling to Porto Santo and Tenerife (Canary Islands, Spain) to make geological observations (Bouheiry, 2013). On his return to Madeira in the winter of 1853/54, he met the English geologist Charles Lyell (1797Lyell ( -1875 that had travelled to Madeira to study the geology of the Atlantic Islands. According to Wilson (2007), Lyell went to Madeira to evaluate the catastrophist 40 theory of 'craters of elevation' postulated by Leopold Von Buch (1774 -1853) (Buch, 1826), against his uniformitarian views (Lyell, 1855). Lyell choose Hartung to accompany him due to his geological curiosity, knowledge of the Portuguese language, and the geography of the island. Both travelled to Madeira and to the Canary Islands (Spain) of Tenerife, La Palma and Gran Canaria (Pinto and Bouheiry, 2007;Wilson, 2007). In the winter of 1854 Hartung proceeded alone to explore the Canary Islands of Lanzarote and Furteventura (Bouheiry, 2015). Lacking a formal geological education, in 1855 he took private 45 geology lessons with Gustav von Leonhard (1816-1878) (Bouheiry, 2013).
Hartung planned to publish the geological observations of Madeira and the Canaries archipelagos with Lyell, but due to Lyell's schedule this never came to fruition (Bouheiry, 2013), although a manuscript draft by Lyell with several sketches and illustrations by Hartung does exist (see Lyell and Hartung, 1856, unpublished manuscript). In 1856, during a meeting with scholars in Berlin including Lyell, Hartung was encouraged by Alexander von Humboldt (1769-1859) to travel and study 50 the geology of the Azores Archipelago (Bouheiry, 2015(Bouheiry, , 2013 and he, in fact, travelled to the Azores archipelago in 1857. During his stay in Azores, he produced a manuscript (Hartung, 1857a) on the geology of Terceira Island (see Pinto, 2007).
Having explored the archipelagos of Madeira, Canary and Azores, he proceeds in 1858 to 1861 to explore the volcanic areas of Germany to compare them with his own observations in the Atlantic islands (Bouheiry, 2015). He started to publish his results on Lanzarote and Fuerteventura (Hartung and Arlett, 1858;Hartung, 1857b), on the Azores (Hartung, 1860a, b) and on 55 the Gran Canaria (Hartung, 1862). Hartung further publishes his observations on Madeira and Porto Santo Islands (Hartung and Mayer, 1864), and is co-author in a book about the geology of Tenerife (Fritsch et al., 1867). Due to his work, he receives in 1862 an honorary doctorate from the University of Konigsberg (Reifs, 1891).
Hartung's own geological observations and certainly the influence of Lyell and Heer ideas, led him to provide detailed field evidence against catastrophic theories, pointing out in favour of the gradual upbuild of the Atlantic islands, the formation of valleys by erosion or the uplift movements (Pinto and Bouheiry, 2007). Furthermore, he was also a pioneer in what concerns to collecting geological and paleontological specimens (but also entomological and botanical specimens; see Bouheiry, 2013Bouheiry, , 70 2015, that were delivered mostly to German and Swiss academics for study and description, which were later published in Hartung's own books or in separate papers (e.g. Heer, 1857;Hartung and Mayer, 1864). This legacy allowed, in recent decades, to localize the fossiliferous outcrops described by Hartung almost 200 years ago and to obtain new and important data on the geology of these sites and to collect new fossil specimens (e.g. Madeira et al., 2007;Góis-Marques et al., 2018;Góis-Marques et al., 2019). 75 Despite the perseverance to travel in hard conditions and his publication track, Hartung is still a less-known figure in Geology, and further efforts are needed to put together the life of this explorer. Important data and clues to his scientific views and relations to other fellow geologist and other scientists are certainly to be found in his unpublished correspondence, namely to Heer (Bouheiry, 2013) and in his reports to the 'Hartungsche Zeitung'. As pointed out by Pinto and Bouheiry (2007), the achievements of this German geologist should not be forgotten and should be celebrated as classic works on the geology of 80 the Atlantic Islands.

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Author contributions. All authors contributed equally. 85
Competing interests. The authors declare that they have no conflict of interest.