Revista de la Asociación Geológica Argentina 64 (1): 55 - 59 (2009) 55

THE FIRST GEOLOGICAL MAP OF

Eduardo O. ZAPPETTINI and José MENDÍA

Servicio Geológico Minero Argentino (SEGEMAR) - Av. Julio A. Roca 651 (1322) Emails: [email protected], [email protected]

ABSTRACT This contribution analyses the first geological map of Patagonia drawn by Darwin around 1840, and colour-painted by Darwin himself. It had remained unpublished and only a small version in black and white had been printed before. The different units mapped by Darwin are analysed from a modern perspective, and his ability to show a synthesis of the complex geological structure of Patagonia is stressed.

Keywords: Geological map, Patagonia, Patagonian Shingle, Darwin geologist.

RESUMEN: El primer mapa geológico de la Patagonia. La presente contribución analiza el primer mapa geológico de la Patagonia reali- zado por Darwin cerca de 1840, pintado en colores por el mismo Darwin, que ha permanecido inédito y del que sólo se cono- cía una versión de tamaño reducido en blanco y negro. Se analizan las diferentes unidades mapeadas por Darwin desde una perspectiva actual, destacándose su habilidad para mostrar en esa síntesis la compleja estructura de la Patagonia.

Palabras clave: Mapa geológico, Patagonia, Rodados Patagónicos, Darwin geólogo.

DARWIN AND THE VOYAGE OF HMS BEAGLE

At the time set sail on board HMS Beagle on a journey that was to last two years and ended up lasting five, he was not more than an amateur naturalist that had quitted his medical courses and after that abandoned his in- tention of applying for a position in the Church of England, just to embrace the study of natural history. In those years (1830-1833) published his theory of gradualism (the present is the key of the past) as a counterpart to catastro- phism then prevailing in geological thought. During the five years (1831- 1835) that his journey on board HMS Beagle lasted - of which three years and one month were spent ashore - Darwin made countless observations on geology and and even on the communi- ties that he visited (Fig. 1). These altoge- ther paved the way towards his famous theory on and of species and the influence that the en- vironment - including its geological cons- Figure 1: Itinerary of HMS Beagle and landings and titution and - has on the suc- journeys of Charles Darwin cess and adaptability of species. in the interior of South America. 56 E. O. ZAPPETTINI AND J. MENDÍA

DARWIN'S CONTRIBUTIONS on the topography produced by (1826- of gneiss and granitic slates that compri- TO GEOLOGICAL 1830) and published in London by John se the Cordillera presently bearing his KNOWLEDGE Murray. The watercolour is from the time name (Eastern Metamorphic Complex of of Darwin's voyage on the Beagle or Aysen and Magallanes in and La- Darwin's contributions to the geological maybe just a few years later, circa 1840. pataia Formation in Argentina). Towards knowledge of South America were re- On the back of the map there is an anno- the northeast he pointed out the predo- corded in four main papers, i.e., On the tation reading "p 94", which suggests minance of gneiss and granites (Coast connection of certain volcanic phenomena in that it was drawn for inclusion as an illus- Batolith in Chile). Between Cabo Tres South America (1838), On the distribution of tration to one of the volumes of the Montes and the north of the Chonos erratic boulders and on the contemporaneous Geology of the voyage of H.M.S. Beagle Islands the predominant rock is a Mica stratified deposits of South America (1841), (1846c), but it was never printed. slate with organic matter (presently Canal An account of the fine dust which often falls on The only previous regional maps are tho- King Formation). vessels in the Atlantic Ocean (1846a,[Read 4 se published by d'Orbigny (1842) toge- June 1845), On the Geology of the Falkland ther with the geological sketch of the UNIT 2 (Trappean rock and porphyries). It Islands (1846b), and finally the book Geo- provinces of Misiones, Corrientes, Entre includes intrusive and extrusive rocks logical Observations on South America (1846c) Ríos, Santa Fe, and Buenos Aires, inclu- exposed in Hoste and Londonderry reprinted in 1876 as part of his Geological ding northern Patagonia down to Valdés Islands (Chile) and also Mesozoic ophio- observations on the volcanic islands and parts of Peninsula. litic rocks exposed in Wollaston Island. the South America visited during the voyage of It comprises Paleogene monzodiorites, H.M.S. Beagle. On the other hand, a first GEOLOGICAL MAP diorites and gabros and Mesozoic basal- unpublished essay of his geological ob- OF PATAGONIA tic lavas of the Hardy Formation, and the servations was written during his voyage Sarmiento and Tortugas ophiolitic com- on board H.M.S. Beagle ca. 1834 which is The observations by Darwin recorded on plexes in Chile. titled Reflection on reading my geological notes. the map are mainly referred to coastal In Wollaston Island Darwin described In this work Darwin put forward a the- areas surveyed by HMS. Beagle (Fig. 2) "greenstones" with pyrite and epidote with ory on the geological formation of South and involve seven geological units: evidence of metamorphism, and basaltic America and included his interpretations submarine volcanic rocks. In Hardy Pe- on the history of life in the continent 1) Granite, Mica slate, ninsula he recorded the pyrite-rich "trap- which, albeit not evolutionist is neverthe- 2) Trappean rock and porphyries, pean and basaltic rocks", trachytes with less sequential (cf. S. Herbert 1995). 3) Purple porphyries and infra metamorphics, columnar jointing, and diorites rocks. In these works there are numerous and 4) Clay slate, Darwin's precise drawing of the contact detailed descriptions of geological units. 5) Tertiary [newer - crossed out -] (?), between this unit and Unit 1 is especially However, figures representing his obser- 6) Recent, remarkable when compared to modern vations are few and of limited interest. 7) Basaltic lava. maps. Despite of this, Darwin at some stage of About units 2 and 3 he states "These two his life as a scientist tried to synthesize in are perhaps very closely allied". UNIT 3 (Purple porphyries and infra meta- a map the main units that were subject of morphics). This unit was recognized by his work, although such a map was never UNIT 1 (Granite, Mica slate). It mainly Darwin on the coast of Santa Cruz. It published. involves the so-called Coast comprises the volcanic rocks of the The Library at Cambridge University Batolith that Darwin stated as exposed in Chon Aike Formation, which in this sec- keeps an original unpublished map pain- Chilean Patagonia south of the Strait of tor represents the easternmost exposures ted with water-colours by Darwin him- Magellan. It includes outcrops at the of the Deseado Massif. Darwin descri- self. This is the earliest known Regional notheastern corner of Hoste Island and bed these volcanics as trachytic porphy- Geological Map of the Patagonian re- at the northwestern sector of Navarino ries. The unit includes the tectonic silici- gion of Chile and Argentina (Fig. 2). A Island. In this unit are also included the fied breccias assigned to the Bahía Laura black and white version was published by Mica slates of the southernmost end of Group, and exposed at Cabo Blanco. Rhodes (1991, Fig. 3) who stated "the the Chonos Archipelago in the Taitao These were erroneously interpreted by magnificent structure of this map" in contrast and Tres Montes peninsulas. Darwin as siliceous sedimentary rocks with the other Darwin's unpublished In his description of this unit Darwin and compared them to those of the Mal- map of Patagonia which is rather simple recorded different lithologies, among vinas Islands. (Herbert 1991 and 2005, plate 6). The which he distinguished - west of the Off-limits he describes purple to pink, geological observations were represented bifurcation - a complex and sometimes laminated, porphyric The first geological map of Patagonia 57

Figure 2: Geologic map of Patagonia (Darwin, circa 1840, unpublished). rocks, which are slightly vesicular with north and points out the presence of Navarino Island. He describes slates ex- feldspar and quartz crystals. He stated local chert beds. posed along the Beagle Channel between these as the dominant rocks in between its bifurcation and Lemaire Strait, consti- Port Santa Elena, Camarones and Ma- UNIT 4 (Clay slate). According to Dar- tuting Navarino Island to the south and laspina up to the "Paps of Pineda" (sic). win's description, it comprises siltstones, the eastern sector of Hoste Island and At Puerto Deseado he records the pre- feldspar volcanics, graywackes, scarce Hardy Peninsula. North of the Beagle sence of porphyries up to 40 km west of black limestones with Lower Cretaceous Channel this unit runs in a northwestern the coast, covered by Tertiary deposits. remains, and metamorphic schists. direction towards Brunswick Peninsula He indicates that the composition is These are the core of the mountain ran- on both coasts of Admiralty Strait, con- similar to that of those described further ges of southern and tinuing north along the eastern flank of 58 E. O. ZAPPETTINI AND J. MENDÍA

the Cordillera. Darwin collected his description he indicates that not all ral inability to translate his images into visual from the limestone beds he recorded. the gravel beds are from recent times, representations". These indicate a Cretaceous age. particularly those of higher tablelands Lastly, it should be stressed that if it had Darwin stressed the change in the direc- (see discussion in Martínez et al. 2009). been published when originally planned, tion of the Cordillera, that north of the He recorded interesting observations on it would have constituted a singular in- runs with a N-S orien- the origin and transport mode of the gra- itial contribution to the geological carto- tation changing south of it to a E-W vels, noting the difficulty in explaining graphy of the South American conti- orientation. This unit includes the pre- the distribution covering the entire area nent. sent Lemaire and Yaghan Formations in from the Andes to the coast. He did Argentina and Cerro Toro, Yaghan and point out, however, that the present dis- WORKS CITED IN THE TEXT Punta Barrosa Formations in Chile, tribution of the gravels was due to mari- spanning the Late -Cretaceous ne action. Casadío, S. and Griffing, M. 2009. Sedimentology (see Olivero et al. 2009). and Paleontology of a Miocene marine suc- Again, we must stress the precision with UNIT 7 (Basaltic lava). It represents the cession frst noticed by Darwin at Puerto De- which Darwin drew the contact between basaltic exposures along the middle and seado (Port Desire). Revista de la Asociación units 2 and 4 in Tierra del Fuego. upper course of the Río Santa Cruz and Geológica Argentina 64 (1): 83-89. the Meseta La Siberia. Darwin placed Darwin, C. 1838. On the connexion of certain UNIT 5 (Tertiary, Pliocene?). Darwin inclu- these outcrops as contemporaneous of volcanic phaenomena, and on the formation des here the Tertiary units exposed in the higher sections of the Tertiary for- of mountain-chains and volcanos, as the ef- extra-Andean Patagonia right across to mation. In fact, the basalts are of a Plio- fects of continental elevations. Proceedings the coast of Santa Cruz. He observes cene-Quaternary age (see Streling and of the Geological Society 2: 654-660, Lon- that these overlie porphyries of Unit 3. Malagnino 2009) and include the units don. In the map, he represents this unit in the presently called Meseta de las Vizcachas Darwin, C. circa 1840. Geological Map of Pa- hills of northern Tierra del Fuego and in Basalt and La Siberia Formation. tagonia image from the Cambridge University the northern areas of Brunswick Penin- In his observations he states that the out- Library (Manuscript MS.DAR.44:13). Availa- sula. Darwin's observations on this unit crops predominate on the Northern side ble at the Keeping time exhibition web-site: include the identification of several fau- of the Río Santa Cruz valley and that http://www.lib.cam.ac.uk/exhibitions/Keepi nal assemblages with abundant , they reach the foothills of the Andes. He ng_Time/images/large/darwin.jpeg Pecten and Ostrea. He called this complex recorded that the basalts were olivinic Darwin, C. 1841. On the distribution of erratic the "Patagonian Tertiary Formation" (see and that columnar disjunction was com- boulders and on the contemporaneous uns- Parra and Griffin 2009, Casadío and mon. He identifies at least three overl- tratified deposits of South America. Proce- Griffin 2009). ying beds. Acknowledging the great edings of the Geological Society 3(2): 425- From a lithologic point of view he recog- extension covered by the exposures he 430, London. nized the presence of beds with pumice- concludes that "This great deluge of lava is Darwin, C. 1845. Journal of researches into the ous siltstone with abundant gypsum, worthy, in its dimensions, of the great continent natural history and geology of the countries sandstones, and claystones with calcare- to which it belongs. The aggregate streams have visited during the voyage of H.M.S. Beagle ous concretions. At the headwaters of flowed from the Cordillera to a distance (unpa- round the world, under the Command of the Santa Cruz River he observed that ralleled, I believe, in any case yet known) of Capt. Fitz Roy, R.N. John Murray, 2d. edition, the sedimentary rocks are covered by about 100 geographical miles" (Darwin 1846, 519 p., London. basaltic lavas of unit 7. p. 116) Darwin, C. 1846a. An account of the fine dust which often falls on vessels in the Atlantic UNIT 6 (Recent). This unit represents CONCLUSIONS ocean. Quarterly Journal of the Geological Quaternary deposits that Darwin recog- Society 2: 26-30, London. nized at the southern end of Santa Cruz The brief description presented herein Darwin, C. 1846b. On the geology of the Fal- between the Río Gallegos and Cabo shows one of Darwin's less known fa- kland Islands. Quarterly Journal of the Vírgenes, in the northeastern coast of cets, i.e., his ability to represent his geo- Geological Society 2: 267-279, London. Tierra el Fuego, along both coasts of the logical observations in a map. This con- Darwin, C. 1846c. Geological observations on Strait of Magellan in its northeastern sec- trasts Stoddart (1995) who emphasized, South America. Being the third part of the tor, and in the sector between Useless when analyzing the geological results of geology of , under Bay and Bahía San Sebastián. He includes Darwin's voyage on the Beagle, "the con- the command of Capt. Fitzroy, R.N. during here the "Rodados Patagónicos", which he trast between Darwin's verbal facility in descri- the years 1832 to 1836. Smith Elder and Co. called "Gravel Formation of Patagonia". In bing landscapes and evoking mood, and his gene- 280 p., London. The first geological map of Patagonia 59

Darwin, C. 1876. Geological observations on the observations on the Patagonian Shingle Strelin, J. and Malagnino, E. 2009. Charles Dar- volcanic islands and parts of South America Formation ("Rodados Patagónicos"). Revista de win and the oldest glacial events/episodes in visited during the voyage of H.M.S. 'Beagle'. la Asociación Geológica Argentina 64(1): 90- Patagonia: the erratic blocks of the Río Santa 2d ed. Smith Elder & Co. 648 p., London. 100. Cruz Valley. Revista de la Asociación Geo- D'Orbigny, A. 1842. Voyage dans l'Amérique Mé- Parras, A. and Griffin, M. 2009. Darwin's Great lógica Argentina 64(1): 101-108. ridionale. Bertrand ed., 3(Géologie), 290 p., Tertiary Patagonian Formation at the mouth Paris. of the Río Santa Cruz: a reappraisal. Revista Herbert, S. 1991. Darwin as a prospective geolo- de la Asociación Geológica Argentina 64(1): gical author. British Journal for the History of 70-82. Science 24: 159-192. Olivero, E.O., Medina, F.A., and López C., M.I. Herbert, S. 1995. From Charles Darwin's Port- 2009. The stratigraphy of Cretaceous muds- folio: An early essay on South American tones in the Eastern Fuegian Andes: New Geology and species. Earth Sciences History data from body and trace fossils. Revista de la 14(1): 23-36. Asociación Geológica Argentina 64(1): 60-69. Herbert, S. 2005. Charles Darwin, Geologist. Rhodes, F.H.T. 1991. Darwin´s search for a the- Cornell University Press. 485 p., Ithaca. roy of the earth: symmetry, simplicity and Lyell, C. 1830-1833. Principles of Geology. John speculation. British Journal for the History of Murray 1(1830) 511 p.; 2(1832) 330 p.; Science 24: 193-229. 3(1833) 109 p., London. Stoddart, D. 1995. Darwin and the Seeing Eye: Martínez, O.A., Rabassa, J. and Coronato, A. Iconography and Meaning in the Beagle Recibido: 3 de octubre de 2008 2009. Charles Darwin and the first scientific Years. Earth Sciences History 14(1): 3-22. Aceptado: 4 de noviembre de 2008