The circular reef of coral, the work of ancient Polyps, foreshadows the atolls of the great ocean, for it was during the Jurassic period that the Polyps of the ancient world were most active in the production of coral-reefs and islets.
The observations of Mr. Darwin on theatolls of the Pacific, prove that such a continuous subsidence is probable.
For the entire remainder of the war these planes pounded the by-passed atolls with such power that the Japanese on them were eliminated from any further role in the war.
And what explanation does it afford of the fact that, in some parts of the ocean, only atolls and encircling reefs occur, while others present none but fringing reefs?
And it is at once obvious that the lines of active volcanoes lie around the margins of the areas occupied by the atolls and the encircling reefs.
The structure of the rocky accumulation in the encircling reefs and in the atolls is essentially the same as in the fringing reef.
Clearly, only in one of two ways: either the sea must have risen over those areas which are now covered by atolls and encircling reefs; or, the land upon which the sea rests must have been depressed to a corresponding extent.
Appended to Mr. Darwin's great work on coral reefs, there is a map on which atolls and encircling reefs are indicated by one colour, fringing reefs by another, and active volcanoes by a third.
And no one has yet shown that any such great melting of polar ice, and consequent raising of the level of the water of the ocean, has taken place since the existing atolls began to be formed.
Atolls may be produced also by the backward drift of sand from either end of a crescentic coral reef or island, the spits uniting in the quiet water of the lee to inclose a lagoon.
In very many instances, however, atolls and barrier reefs may be explained without subsidence.
In much the same way atolls may be built on any shoal which lies within the zone of coral growth.
We can further see how it arises that the atolls in the Pacific and Indian Oceans extend in lines parallel to the generally prevailing strike of the high islands and great coast-lines of those oceans.
The geographer Balbi has in effect described those barrier-reefs, which encircle moderately sized islands, by calling them atolls with high land rising from within their central expanse.
The apparent progressive disseverment in the Maldiva Archipelago of large atolls into smaller ones, is, in many respects, an important consideration, and requires an explanation.
We have as yet only considered the origin of barrier-reefs and atolls in their simplest form; but there remain some peculiarities in structure and some special cases, described in the two first chapters, to be accounted for by our theory.
Several theories have been advanced to explain the origin of atollsor lagoon-islands, but scarcely one to account for barrier-reefs.
The fact of soundings having been obtained between two separate and perfectly characterised atolls is in itself interesting, as it has never, I believe, been effected in any of the many other groups of atolls in the Pacific and Indian seas.
It consists of seventeen atolls with an immense number of islands, of which some three hundred are inhabited.
Those of the central division, comprising the atolls between North Male and Haddumati, who are under the direct rule of the sultan, and have been more exposed to Arab influences.
Further west the Cosmoledo and Comoro Islands consist of atolls and islands surrounded by barrier reefs; and these bring us pretty close to the present shores of Africa and Madagascar.
The surface of the atolls is covered with sand, except in a few places where it has been turned into soil through the admixture of decayed vegetation.
The group consists of a number of atolls ranged in two almost parallel lines, which run from N.
These atolls are of coralline formation and of irregular shape.
The atollsare all about the same shape--that is, circular.
Islands were on every side of us, high rugged peaks, some of them a hundred miles away, and near us small low atolls covered with a riotous growth of cocoanuts.
Even had we wanted to anchor, it seemed impossible, for the openings made by the run of the tide as it ebbed and flowed were too small for us to enter, and the reefs around the outside of the atolls were too rough for us to give a thought to.
I have since entered, I suppose, some dozen atolls in different parts of the Pacific, and the experience has never been repeated.
On the sea-side and in certain atollsthis profusion of vitality is even shocking: the rock under foot is mined with it.
In no quarter are the atolls so thickly congregated, in none are they so varied in size from the greatest to the least, and in none is navigation so beset with perils, as in that archipelago that we were now to thread.
The border of land circumscribing the lagoon was in many places low and narrow, consisting chiefly of a reef or beach of rocks; in other words, it was one of the coralline atolls described on p.
Coral atolls with waving palm trees are delightful spots when one reads of them when seated in a comfortable armchair in a snug library, but the real island comes down heavily upon the nerve-centres when night falls upon the spot.
These atolls abound in the Pacific Ocean, and rising but a few feet above the surface, surrounded by uncertain and uncharted currents, are the dread of navigators.
Near the centre of the North Pacific and near the western end of the chain of atolls above mentioned, are two small sand islands in the usual lagoon, with a coral reef enclosing both.
Here we again had an opportunity of observing the configuration of which all known atolls furnish examples, viz.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "atolls" in a variety of sentences. We hope that you will now be able to make sentences using this word.
