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 / [Charles Darwin].
- Charles Darwin
- Date:
- 1842
Licence: Public Domain Mark
Credit: 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 / [Charles Darwin]. Source: Wellcome Collection.
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![the whole sank down, from a basis formed of other corals and their consolidated fragments. Thus the difficulty on this head, which before seemed so great, disappears. As the space between the reef and the subsiding shore continued to increase in breadth and depth, and as the inju- rious effects of the sediment and fresh water borne down from the land were consequently lessened, the greater number of the channels, with which the reef in its fringing state must have been breached, especially those which fronted the smaller streams, will have become choked up by the growth of coral: on the windward side of the reef, where the coral grows most vigorously, the breaches will probably have first been closed. In barrier-reefs, therefore, the breaches kept open by draining the tidal waters of the lagoon-channel, will generally be placed on the leeward side, and they will still face the mouths of the larger streams, although removed beyond the influence of their sediment and fresh-water;— and this, it has been shown, is commonly the case. Referring to the following diagram, in which the newly- formed barrier-reef is represented by unbroken lines, instead of by dots as in the former woodcut, let the work of subsi- dence go on, and the doubly-pointed hill will form two small ^ g' ^ [No. 5.] A'A'—Outer edges of the barrier-reef at the level of the sea. The cocoa-nut trees represent coral-islets formed on the reef. C C—The lagoon-channel. B' B'—The shores of the island, generally formed of low alluvial land and of coral detritus from the lagoon-channel. A A—The outer edges of the reef now forming an atoll. Q'—The lagoon of the newly-formed atoll. According to the scale, the depth of the lagoon and of the lagoon-channel is exaggerated.](https://iiif.wellcomecollection.org/image/b29331213_0118.jp2/full/800%2C/0/default.jpg)
