STRUCTURE OF CORAL ISLANDS. 173 



five and six hundred fathoms, the line was partty cut as if it 

 had rubbed against a projecting ledge of rock ; and deduces 

 from the fact "the probable existence of submarine cliffs." 



Prof. Agassiz states that the Bahamas and the reefs 

 northeast of Cuba have very great depth close alongside. 



There are examples also of less abrupt slopes. Northwest 

 of the Hawaian Group, Captain Lisiansky, who commanded 

 the Russian ship Neva in a voyage round the world in the 

 years 1860-61, at the island bearing his name, found shallow 

 water for a distance of six or seven miles ; the water deepened 

 to ten or eleven fathoms the first mile, fifteen the second, and at 

 the last throw of the lead there were still but twenty-five fath- 

 oms. Christmas Island affords on its western side another exam- 

 ple of gradually deepening waters. Yet these shallow waters 

 terminate finally in a rapid declivity of forty or fifty degrees. 



Off the prominent angles of an atoll, soundings gen- 

 erally continue much beyond the distance elsewhere, as was 

 first observed by Beechey. At Washington Island, mostly 

 abrupt in its shores, there is a bank, according to the surveys 

 of the Expedition, extending from the east point to a distance 

 of half a mile, and another on the west extending to a distance 

 of nearly two miles. At Kuria, one of the Kingsmills, sound- 

 ings continue for three miles from the north extremity, along 

 a bank stretching off from this point to the north-northwest. 

 Many other instances might be cited, though they are seldom as 

 remarkable ; yet nearly all islands, especially if the points are 

 much prominent, afford similar facts. The Florida reefs, 

 according to Prof. Agassiz, have a gradual slope to seaward 

 instead of the abruptness of the Bahamas. As corals may 

 grow on submerged land of any form, there is no reason 

 why the bottom around should not often deepen gradually. 

 It has been said that the reef to leeward is generally less 



