NATUEAL SCIENCE NEWS. 



current of warm air is formed, car- 

 rying up moisture 'into the colder 

 regions of the atmosphere, where 

 it is condensed and forms clouds. 

 A similar phenomenon is observed 

 in our western plains, where the 

 sky is frequently clear early in the 

 morning, but by 10 or n o'clock 

 enough heat has been accumulated 

 to cause the formation of clouds. 



The islands of the Pacific are of 

 two kinds, called the lower and 

 the higher. The lower rise but 

 7, 10, and rarely as high as 100, 

 feet above the level of the sea; 

 while the higher islands reach an 

 elevation of 10,000, 12,000, and 

 even 15,000 feet. There is no 

 transition between them. The 

 most remarkable are the lower is- 

 lands. Their appearance is very 

 peculiar. In the first place, the 

 eye is arrested by a white beach; 

 then comes a line of verdure, due 

 to tropical trees; then a lagoon of 

 quiet water of a whitish or a yel- 

 lowish color; then another line of 

 verdure, and finally, beyond all, 

 the dark blue waves of the ocean. 

 A picture of Whitsuntide Island 

 illustrated the structure. It is a 

 ring rising 7 or 8 feet above the 

 sea level, enclosing a lagoon, and 

 presenting the characteristics just 

 described. The lagoon inside is 

 but a few fathoms deep; but on the 

 outside of the island, the water is 

 15,000 feet deep. Here then we 

 have a tower-like structure reach- 

 ing up from the bottom of the sea, 

 and having a depression in its 

 summit. Some of these lower is- 

 lands are 50 miles across, but most 

 of them are not so large. In some 

 the ring is broken at several points 

 and these are designated by the 

 Malay word 



The island of Tahiti, the princi- 

 pal one of the Society Islands, is 

 a good example of the second class 

 or higher islands. It rises 7,000 

 to 8,000 feet above the level of the 

 sea, has no lagoon in its center, 

 but a crater, and the water around 

 it is very deep. It may in fact be 

 considered as a mountain rising to 

 a height of some 18,000 feet from 

 the bottom of the sea. Outside of 

 it is a double girdle of low islands, 

 one near, which Darwin calls a 

 fringing reef, and one further out, 

 to which he gives the name of a 

 barrier reef. 



On examining these reefs and 

 the lower islands their structure 

 will be found made up entirely of 

 animal remains, generation after 

 generation having left their homes, 

 consisting of limestone to accumu- 

 late there. On the top we find 

 these animals living and growing, 



in all colors, shapes, and sizes. 

 The higher islands, on the con- 

 trary, except those near the conti- 

 nent, like Borneo, Sumatra, etc., 

 are entirely volcanic, and do not 

 contain sandstone, granite, or 

 gneiss, like the mountains of the 

 continent. 



The limestone of the lower is- 

 lands is not due to sedimentary de- 

 posits from the ocean, but is the 

 work of the coral animal, the great 

 architect of the sea. According to 

 Agassiz's description, which is 

 here followed, these animals are 

 but a sac, like the finger of a glove, 

 only more leathery. Around the 

 mouth is a series of tentacles, 

 formed by a prolongation of the 

 skin. They are all skin, in fact, 

 and have no special organs, yet 

 they digest food with tremendous 

 rapidity, absorbing it directly. It 

 makes no difference if you turn 

 them inside out; they will digest 

 just as well as before. You can- 

 not kill them by dividing them; 

 for they live all over, like a plant. 

 For this reason they have been 

 called zoophytes. If you cut one 

 into eight parts, each part will live 

 and set up in business for itself. 

 Like all other animals, however, 

 they grow out of eggs. The eggs 

 are formed within the skin, which 

 is double, and divided into cells by 

 partitions or septa. When mature, 

 they detach themselves, move 

 about in the water, until they find 

 a favorable place, and then estab- 

 lish a new colony. They do not 

 contribute to the growth of their 

 parent colony, which is effected in 

 another way. 



On examining a piece of coral, it 

 is seen to be full of little holes, 

 popularly supposed to be the 

 places for the stomachs of the ani- 

 mals, but this is not so at all; the 

 coral animal does not form a secre- 

 tion around it like the mollusks, 

 but inside, between the two folds 

 of its skin. Coral is, therefore, 

 the bones and not the skull of the 

 animal. As before stated, these 

 animafs work in societies or colo- 

 nies, and their tendency is to re- 

 peat the forms peculiar to each 

 species; thus we have corals shap- 

 ed like a hand, like the branches 

 of trees, like mushrooms, like a 

 brain with its convolutions. They 

 grow and multiply in these soci- 

 eties by budding and gemmation. 

 The side of the animal begins to 

 bulge out, and the protuberance 

 so formed develops into a new 

 mouth, which soon eats and di- 

 gests for itself, but does not sepa- 

 rate from its parent. This process 

 goes on symmetrically, and pro- 



duces the variety of regular shapes 

 thus described. 



Some distance below the sur- 

 face, we no longer find these beau- 

 tiful shapes, but a dense coral 

 rock. Take for instance the coral 

 reefs of Florida. Beginning 120 

 feet below the surface, we first find 

 about 30 feet of massive rock, then 

 the astraea, then the meandrina, 

 and about ten feet below the sur- 

 face the palmata or hand-shaped 

 coral. In the mud between the 

 reefs and the continent there are 

 multitudes of branching corals of 

 the most beautiful forms, colors 

 and delicacy of structure. The 

 production of coral rock is explain- 

 ed partly by the mechanical action 

 of the waves, and partly by the de- 

 struction of the coral insect by the 

 sea urchin and other 'animals feed 

 on it. The waves disintegrate the 

 structure formed by the animal, 

 and then roll back the coral sand 

 thus produced upon it, where it 

 undergoes a process of induration 

 in the course of time. 



It is an interesting question how 

 the structure ever rises above the 

 water level, seeing that the animal 

 which makes it cannot live out of 

 the water. The little architects 

 retain enough sea water to last 

 them over until the next tide and 

 are so enabled to work up to the 

 highest watermark. Actinia have 

 been observed all closed up on the 

 rock at low w r ater, and then sud- 

 denly opened like magnificent 

 flowers, 5 and 6 inches in diame- 

 ter, when the tide rose. 



The ring form of the Pacific is- 

 lands is due to the shape of the 

 foundation upon which the coral 

 animals built. On the Florida 

 coast the reefs run parallel to the 

 land for the same reason. Now 

 take this, together with the fact 

 that all the high islands are vol- 

 canoes, with the regular conical 

 shape, and you will be prepared to 

 understand the explanation, given 

 simultaneously by Darwin and 

 Dana, that the low islands were 

 originally reefs around the high is- 

 lands or volcanoes, and that the 

 latter, by the gradual subsidence 

 of the ocean bed, sank and left the 

 reefs appear as low islands, with a 

 lagoon where the crater of the vol- 

 cano was. The reefs, of course, 

 were gradually carried down along 

 with the mountain upon the sides 

 of which they rested, but the coral 

 insects kept on building towards 

 the surface; the mountain appear- 

 ed as a smaller and smaller cone 

 in the center; what was left a 

 fringing reef now became a barrier 

 reef, and the mountain finally dis- 



