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Geological Observations on the Volcanic Islands

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Geological Observations on the Volcanic Islands, visited during the Voyage of H.M.S. Beagle
AuthorCharles Darwin
LanguageEnglish
GenreGeology
Publication date
1844
Media typeBook

Geological Observations on the Volcanic Islands, visited during the Voyage of H.M.S. Beagleis a book written by the EnglishnaturalistCharles Darwin.The book was published in 1844, and is based on his travels during thesecond voyage of HMSBeagle,commanded by captainRobert FitzRoy.It is the second book in a series ofgeologybooks written by Darwin that also includesThe Structure and Distribution of Coral Reefs(published in 1842) andGeological Observations on South America(published in 1846).[1]

The text contains seven chapters, and includes observations made during Darwin's travels to the volcanic island ofSt. JagoinCape Verde,theFernando de Noronhaarchipelago,Ascension Island,the island ofSaint Helena,theGalápagos Islands,James Island,New Zealand,Australia,Van Diemen's Land,and theCape of Good Hope.[1]

The book includes one of the earliest accounts of the process ofmagmatic differentiation.[2]While observing abasalticlava flowin theGalápagos Islands,Darwin observed that "crystals sink from their weight"[3][note 1]and that this "throws light on the separation of the high silica versus low silica series of rocks."[2]This was the first proposal of thefractional crystallizationhypothesis of magma differentiation that was further developed and demonstrated in the 20th century.[2]

Charles Darwin wroteGeological Observations on the Volcanic Islandsas part of a series of books on geology.

The geologistArchibald Geikiepraised the book, calling it "the best authority on the general geological structure of most of the regions it describes," and that Darwin was "one of the earliest writers to recognize the magnitude ofdenudationto which even recent geological accumulations have been subjected. "[4]

A second edition of the book, published in 1876, combinesGeological Observations on the Volcanic IslandswithGeological Observations on South America.[4]

References

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  1. ^abDarwin, Charles (1846).Geological Observations on South America.p. iii.
  2. ^abcEncyclopedia of Volcanoes.Academic Press. 1999. p. 33.ISBN9780080547985.
  3. ^Darwin, Charles (1844). "Chapter 6".Geological Observations on the Volcanic Islands visited during the Voyage of the H.M.S. Beagle.pp.117–129.Available on-line at:Internet Archive
  4. ^abDarwin, Charles (1901).The Life and Letters of Charles Darwin.D. Appleton. pp. 294–295.
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Notes

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  1. ^Onp. 117of hisGeological Observations on the Volcanic Islands…(1844), Darwin noted the precipitation of albite crystals within basaltic lava on Santiago Island (or "James Island" ) of the Galápagos Islands. He then cited a work by "von Buch" (German geologist and paleontologistChristian Leopold von Buch(1774–1853)):Physikalische Beschreibung der canarischen Inseln[Physical description of the Canary Islands] (Berlin, 1825), which was translated into French as: Léopold von Buch, with C. Boulanger, trans.,Description physique des Îles Canaries(Paris, France: F. G. Levrault, 1836). Darwin citedpp. 190–191of that translation, where Buch mentions a similar geological formation on the island ofTenerifein the Canary Islands and where he mentions a "M. de Drée", who had found experimentally that feldspar crystals form and precipitate in molten lava:"Les expériences de M. de Drée, dans lesquelles il a fait fondre diverses laves dans un creuset, ont prouvé que dans une telle masse fluide, les cristaux de feldspath devaient tendre à se précipiter au fond."(The experiments of M. de Drée, in which he melted various lavas in a crucible, proved that in such a fluid mass, crystals of feldspar should tend to precipitate to the bottom.) "M. de Drée" was Étienne-Marie-Gilbert, Marquis de Drée (1760–1848) [Fr], a French amateur geologist who in 1808 had presented toL'Institut national de Francehis paper"Mémoire sur un nouveau genre de liquéfaction ignée qui explique la formation des laves lithoïdes"(Memoir on a new type of igneous liquefaction that explains the formation of stony lavas). (Summarized (in French) in: Etienne-Marie-Gilbert Drée (1808 March 28)"Mémoire sur un nouveau genre de liquéfaction ignée qui explique la formation des laves lithoïdes,"Nouveau Bulletin des Sciences,1:137–142.)On pp. 16–17 of the memoir,Drée stated:"En plaçant le morceau de porphyre dans le creuset no. 6, je suis certain que ce morceau touchoit au fond du creuset, et cependant on voit dans le produit tous les cristaux réunis dans la partie supérieure, preuve que la liquéfaction a été assez complète pour permettre l'élévation des cristaux de feld-spath (1)."(In placing the piece of porphyry in crucible number 6, I'm certain that that piece touched the bottom of the crucible, and yet one sees in the product all of the crystals clustered in the upper part — proof that the liquefaction was complete enough to permit the rising [i.e., floating] of the crystals of feldspar(1).) Thus, although Drée had expected the feldspar crystals to float, they instead sank to the bottom of the molten lava — just as had happened in the lavas of James Island and Tenerife.
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