page_title: The Structure and Distribution of Coral Reefs
section_title: Darwin's investigations to test his theory
hierarchical_section_title: The Structure and Distribution of Coral Reefs / Darwin's investigations to test his theory
caption_attribution_description: Lagon de Papeete
context_page_description: The Structure and Distribution of Coral Reefs, Being the first part of the geology of the voyage of the Beagle, under the command of Capt. Fitzroy, R.N. during the years 1832 to 1836, was published in 1842 as Charles Darwin's first monograph, and set out his theory of the formation of coral reefs and atolls. He conceived of the idea during the voyage of the Beagle while still in South America, before he had seen a coral island, and wrote it out as HMS Beagle crossed the Pacific Ocean, completing his draft by November 1835. At the time there was great scientific interest in the way that coral reefs formed, and Captain Robert FitzRoy's orders from the Admiralty included the investigation of an atoll as an important scientific aim of the voyage. FitzRoy chose to survey the Keeling Islands in the Indian Ocean. The results supported Darwin's theory that the various types of coral reefs and atolls could be explained by uplift and subsidence of vast areas of the Earth's crust under the oceans.
context_section_description: By the time that the Beagle set out for the Galápagos Islands on 7 September 1835, Darwin had thought out the essentials of his theory of atoll formation. While he no longer favoured the concept that atolls formed on submerged volcanos, he noted some points on these islands which supported that idea: 16 volcanic craters resembled atolls in being raised slightly more on one side, and five hills appeared roughly equal in height. He then considered a topic which was compatible with either theory, the lack of coral reefs around the Galápagos Islands. One possibility was a lack of calcareous matter around the islands, but his main proposal, which FitzRoy had suggested to him, was that the seas were too cold. As they sailed on, Darwin took note of the records of sea temperature kept in the ship's "Weather Journal".
  He had his first glimpse of coral atolls as they passed Honden Island on 9 November and sailed on through the Low or Dangerous Archipelago (Tuamotus). Arriving at Tahiti on 15 November, Darwin saw it "encircled by a Coral reef separated from the shore by channels & basins of still water". He climbed the hills of Tahiti, and was strongly impressed by the sight across to the island of Eimeo, where "The mountains abruptly rise out of a glassy lake, which is separated on all sides, by a narrow defined line of breakers, from the open sea. – Remove the central group of mountains, & there remains a Lagoon Isd." Rather than recording his findings about the coral reefs in his notes about the island, he wrote them up as the first full draft of his theory, an essay titled Coral Islands, dated 1835. They left Tahiti on 3 December, and Darwin probably wrote his essay as they sailed towards New Zealand where they arrived on 21 December. He described the polyp species building the coral on the barrier wall, flourishing in the heavy surf of breaking waves particularly on the windward side, and speculated on reasons that corals in the calm lagoon did not grow so high. He concluded with a "remark that the general horizontal uplifting which I have proved has & is now raising upwards the greater part of S. America & as it would appear likewise of N. America, would of necessity be compensated by an equal subsidence in some other part of the world."
caption: Darwin saw the coral reef and lagoon around Tahiti.
exif: {"Image Make": "Canon", "Image Model": "Canon EOS 400D DIGITAL", "Image Orientation": "Horizontal (normal)", "Image XResolution": "72", "Image YResolution": "72", "Image ResolutionUnit": "Pixels/Inch", "Image Software": "Microsoft Windows Photo Gallery 6.0.6001.18000", "Image DateTime": "2009:06:01 02:46:07", "Image YCbCrPositioning": "Co-sited", "Image ExifOffset": "248", "Thumbnail Compression": "JPEG (old-style)", "Thumbnail XResolution": "1/96", "Thumbnail YResolution": "1/96", "Thumbnail ResolutionUnit": "Pixels/Inch", "Thumbnail JPEGInterchangeFormat": "5970", "Thumbnail JPEGInterchangeFormatLength": "3793", "EXIF ExposureTime": "1/250", "EXIF FNumber": "10", "EXIF ExposureProgram": "Program Normal", "EXIF ISOSpeedRatings": "200", "EXIF ExifVersion": "0221", "EXIF DateTimeOriginal": "2009:05:18 22:29:46", "EXIF DateTimeDigitized": "2009:05:18 22:29:46", "EXIF ComponentsConfiguration": "YCbCr", "EXIF ShutterSpeedValue": "261023/32768", "EXIF ApertureValue": "108853/16384", "EXIF ExposureBiasValue": "0", "EXIF MeteringMode": "Pattern", "EXIF Flash": "Flash did not fire, compulsory flash mode", "EXIF FocalLength": "24", "EXIF FlashPixVersion": "0100", "EXIF ColorSpace": "sRGB", "EXIF ExifImageWidth": "3888", "EXIF ExifImageLength": "2592", "Interoperability InteroperabilityIndex": "R98", "Interoperability InteroperabilityVersion": "[48, 49, 48, 48]", "EXIF InteroperabilityOffset": "5830", "EXIF FocalPlaneXResolution": "3888000/877", "EXIF FocalPlaneYResolution": "432000/97", "EXIF FocalPlaneResolutionUnit": "2", "EXIF CustomRendered": "Normal", "EXIF ExposureMode": "Auto Exposure", "EXIF WhiteBalance": "Auto", "EXIF SceneCaptureType": "Standard", "EXIF OffsetSchema": "0"}