a point not exceeding one hundred and 

 fifty feet in depth. 



The Coral Reef is not entirely com- 

 posed of living, or even dead corals. 

 The base upon which the corals are liv- 

 ing is as hard and compact as any lime- 

 stone, and the rock of the beach is equal- 

 ly as hard and is formed by the cement- 

 ing together of the coral sand grains. 

 Frequently a pudding-stone or conglom- 

 merate will be formed by the addition 

 of pebbles of various sizes and not in- 

 frequently a beautiful round white rock 

 called oolyte is formed, each sand grain 

 being covered by a calcareous cement. 

 Hence is the name oolyte — egg like. The 

 coral rock has different characteristics 

 according to the position in which it is 

 formed. For example, the rock formed 

 in the lagoon is very compact and con- 

 tains no fossils, while the rock formed 

 on the ocean side is made up of broken 

 pieces of coral, shells, etc. When it is 

 formed in a sheltered place subject to the 

 action of the sea, the rock contains the 

 embedded corals in the positions in which 

 they grew. 



The history or biography of a coral 

 island is as follows: As soon as a sub- 

 merged mountain peak is within one hun- 

 dred and fifty feet of the surface of the 

 ocean the corals begin to grow and in the 

 course of time a vast number of these 

 corals have grown up to the surface of 

 the water. With the corals there also 

 live mollusks, echinoderms, crabs, bryo- 

 zoans and a host of other marine ani- 

 mals. When the coral structure reaches 

 the surface the waves begin their work. 

 The strong winds tear up and break off 

 the corals, pile up the fragments and by 

 their constant motion reduce them to 

 sand. This work continues until a large 

 extent of reef and beach is formed. The 

 under portions become consolidated and 

 form the hard coral rock. The living 

 corals continue growing along the mar- 

 gins of the newly formed island. Thus 

 an island is constructed from the bed of 

 growing corals. As soon as the sand is 

 fine enough to make good earth the seeds 

 of various plants or trees, blown from 

 other islands, perhaps hundreds of miles 

 away, become planted and growing give 

 to the island a covering of vegetation. 



The windward side is always the highest, 

 because the winds act strongest on this 

 side and pile up the debris from the reef. 

 Islands such as the- one just described are 

 constantly forming in the Pacific Ocean, 

 as well as in other Coral Reef seas. 



Coral Reefs are those which border an 

 island or continent and may be divided 

 into two kinds, fringing reefs and bar- 

 rier reefs. The first kind are formed 

 along the edges of the island or conti- 

 nent, while the barrier reefs are formed 

 at some distance from the main land 

 with a body of water, frequently of con- 

 siderable depth, separating them. Many 

 of these fringing and barrier reefs are of 

 large extent, and Mr. James D. Dana, 

 who has made an extensive study of 

 Coral Reefs, gives the following dimen- 

 sions of some well-known localities : The 

 Fiji Islands reefs are from five to fifteen 

 miles wide. Those of New Caledonia 

 lie for one hundred and fifty miles north 

 and fifty miles south of the island, mak- 

 ing a total length of four hundred miles. 

 On the northeastern coast of Australia 

 the reefs extend for one thousand miles, 

 at a distance of from fifty to sixty miles 

 from the coast. These reefs do not, 

 however, all reach the surface of the sea, 

 those portions, which may be seen, being 

 in isolated patches here and there, and 

 many of them are visible only at low 

 water. The largest of these exposed 

 patches does not exceed two miles in 

 width. 



For a long time the cause of the pe- 

 culiar form of the atoll was unknown, 

 but a number of years ago, Mr. Charles 

 Darwin proposed the following plaus- 

 ible theory, based on numerous facts, and 

 now generally accepted. This theory pre- 

 sumes that the Coral Reef began as a 

 fringing reef on the shores of, or sur- 

 rounding an island. This might be, as it 

 is known to be the case with some islands 

 which are submerged mountain peaks. 

 After the coral had formed a fringing 

 reef the island began to slowly sink into 

 the ocean, the coral meanwhile growing 

 upward as rapidly as the island sank, 

 until a barrier reef was formed. This 

 subsidence or sinking continued until 

 the top of the island disappeared and a 

 Coral Reef was built upon it. If the 



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