CONTAINING A DETAILED DESCRIPTION OF THE REEFS AND ISLANDS IN PLATE III. In the beginning of the last chapter I stated the principles on which the map is coloured. There only remains to be said, that it is an exact copy of one by M. C. Gressier, published by the Dépôt général de la Marine, in 1835. The names have been altered into English, and the longitude has been reduced to that of Greenwich. The colours were first laid down on accurate charts, on a large scale. The data, on which the volcanoes historically known to have been in action, have been marked with vermillion, were given in a note to the last chapter. I will commence my description on the eastern side of the map, and will describe each group of islands consecutively, proceeding westward across the Pacific and Indian Oceans, but ending with the West Indies. The WESTERN SHORES OF AMERICA appear to be entirely without coral-reefs; south of the equator the survey of the “Beagle”, and north of it, the published charts show that this is the case. Even in the Bay of _Panama_, where corals flourish, there are no true coral-reefs, as I have been informed by Mr. Lloyd. There are no coral-reefs in the _Galapagos_ Archipelago, as I know from personal inspection; and I believe there are none on the _Cocos, Revilla-gigedo_, and other neighbouring islands. _Clipperton_ rock, 10° N., 109° W., has lately been surveyed by Captain Belcher; in form it is like the crater of a volcano. From a drawing appended to the MS. plan in the Admiralty, it evidently is not an atoll. The eastern parts of the Pacific present an enormous area, without any islands, except _Easter_, and _Sala_, and _Gomez_ Islands, which do not appear to be surrounded by reefs.