a
half to two
On approaching nearer , the whole white beach was distinctly seen ; and above it a narrow belt of land of a light clay colour , surrounding a perfectly smooth lagoon of a beautiful blue tint ; while against the outer belt the surf was breaking with terrific force . The highest part of the land appeared to be about ten or twelve feet above the level of the sea ; and we calculated that the belt between the sea and the lagoon was about seven hundred feet wide , the soil being composed of coral debris and vegetable matter . Besides the palm-trees , there were a few shrubs not more than fourteen or fifteen feet in height . The whole island was about eight miles long , and from one and a half to two miles wide . We sounded as we approached , but could obtain no bottom ; and it was not till we got quite close that the lead gave us ninety fathoms , and farther on seventy , thus proving that the land was the top of a submerged mountain . Such , indeed , are all the islands of this group . Once upon a time in the world 's history , a mountainous region existed on the spot over which we were sailing , which gradually sank till the ocean flowed over all the highest portions .