178 RAMBLES OF A NATURALIST. 



an animal, and which, by their interlacing stems, their 

 variegated branches and budding shoots, can scarcely 

 be distinguished from true vegetables. Enormous 

 dark brown Holothurias were creeping over the sand 

 or climbing slowly up the rocks, waving their crown 

 of tentacles, while beside them lay Star-fishes of 

 bright pomegranate hues, motionless with their ra- 

 diating arms extended around them. Molluscs, resem- 

 bling in form a snail or a slug, although different in size 

 and colour, were dragging themselves slowly onwards 

 like their terrestrial brethren ; while crabs, having 

 the form of enormous spiders, were striding over 

 them in their rapid and sideway course, pausing 

 only from time to time to seize them with their 

 formidable pincers. Other crustaceans, allied to our 

 shrimps and lobsters, sported among the tufted alga3, 



the sea, and thus become uninhabitable to these minute beings. It 

 will readily be understood that in such a case, the mass of the 

 polyparies, on reaching the level of the waves, will, in fact, exhibit 

 a band of reefs surrounding a free space. The debris accumulated 

 on these ridges forms a stratum of mould on their surface, which is 

 soon covered with the rich vegetation of the tropics that grows up 

 from the seeds which the sea or the winds have scattered over this 

 recent soil. 



Mr. Dana, who is one of the most eminent among the American 

 naturalists, has recently offered an explanation of these formations, 

 which at once accounts for the facts, while it explains several 

 objections that present themselves to the preceding theory. This 

 naturalist is of opinion that islands which have been slowly en- 

 gulfed in the sea, actually existed formerly at the same spots 

 where we now find coral islands. The present ring would, there- 

 fore, in this case, mark the limits of the ancient shore. On this 

 hypothesis we can conceive the formation of lagoons thirty miles in 

 diameter, although such a diameter would be remarkable in the 

 case of a crater. (See the works of [Darwin and] Dana on Coral 

 Reefs and Islands.} 



