Narrative of the surveying voyages of his majesty's ships Adventure and Beagle (vol.2- Appendix): between the years 1826 and 1836 : describing their examination of the southern shores of South America, and the Beagles's circumnavigation of the globe

280 APPExnix. Some of the facts which seem to stand most in opposition to the theory that deduces tides in the northern Atlantic from the move- ment of a tide-wave originated in the great southern ocean are : • — the comparative narrowoiess of the space between Africa and Ame- rica ; with the certainty that the sea is neither uniformly nor exces- sively deep in that space,* and the trifling rise of tide ; not only upon either nearest shore (where it does not exceed four or five feet at the utmost), but at Ascension Island, where the highest rise is not two feet.f Secondly, the absence of any regular tide about the wide estuary of the river Plata, the situation and shape of which seems so well disposed for recei%ing an immense tide.i Thirdly, the flood- tide moving towards the west and south along the coast of Brazil, rent from that which we have taken. The course of these lines in the Pacific appears to be altogether problematical ; and though those which are drawn in the neighbourhood of the west coast of America connect most of the best observations, they can hardly be considered as more than conjecture : in the middle of the Pacific I have not even ventured to con- jecture. Tt only remains to add, that 1 shall be most glad to profit by every opportunity of improving this map, and will endeavour to em- ploy for this pui-pose any information with which I may be supplied." pp. 234-5. • Besides the ' Roccas', Fernando de Noronha, and St. Paul rocks, various accounts have been received, from time to time, of shoals near the equator, between the meridians of fifteen and twenty.four degrees west. There can be no doubt, from the descriptions, that many alarms have been caused in that neighbourhood by earthquakes; which are, to my appre- hension, indications of no very great depth of water. In 1761, a small sandy island was said to have been seen by Captain Bouvet, of Le Vail- lant. This, if seen, has probably sunk down since. Krusenstern saw a volcanic eruption thereabouts in 1806. In 1816, Captain Proudfoot, in the ship Triton, fiom Calcutta to Gibraltar, passed over a bank, in lati- tude 0° 32' S. and longitude 17" 46' \V. It appeared to extend in an east and west direction three miles, and in a north and south direction one mile. They sounded in twenty-three fathoms, brown sand ; but saw no appearance of breakers. t At St. Helena it is not three feet : while at Tristan d'Acunha there is a rise of eight or nine feet under ordinary circumstances. { I have passed months in that river without being able to detect any periodical rise of water, which I could attribute to tide ; though it is said, that when the weather is very settled, some indications of a tide may be perceived.