A GREAT LESSON. 243 



cause as peculiar as its effects. Moreover, this cause must be one 

 affecting not merely or only the peculiarities of the animal which 

 builds up the coral, but some cause affecting also the solid rocks and 

 crust of the earth. The coral animals must build on some foundation. 

 They must begin by attaching themselves to something solid. Every 

 coral reef, therefore, whatever be its form — every line of barrier-reef 

 however long — every ring however small or however wide, must in- 

 dicate some corresponding arrangement of subjacent rock. What 

 cause can have arranged the rocky foundations of the coral in such 

 curious shapes ? Extreme cases of any peculiar phenomenon are al- 

 ways those which most attract attention, and sometimes they are the 

 cases which most readily suggest an explanation. Ring-shaped islands 

 of such moderate dimensions that the whole of them can be taken in 

 by the eye, supply such cases. There are atoll-islands where ships 

 can enter, through some break in the ring, into the inner circle. They 

 find themselves in a perfect harbor, in a sheltered lake which no wave 

 can ever enter, yet deep enough and wide enough to hold all the navies 

 of the world. Round about on every side there are the dazzling 

 beaches which are composed of coral sand, and crowning these there is 

 the peaceful cocoanut-palm, and a lower jungle of dense tropical vege- 

 tation. On landing and exploring the woods and shores, nothing can 

 be seen but coral. The whole island is a ring of this purely marine 

 product ; with the exception of an occasional fragment of pumice- 

 stone, which having been floated over the sea from some distant vol- 

 canic eruption, like that of Krakatoa, here disintegrates and furnishes 

 clay, the most essential element of a soil. But reason tells us that 

 there must be something else underground, however deeply buried. 

 When the corals first began to grow, they must have found some rock 

 to build upon, and the shape of these walls must be the shape which 

 was thus determined. One suggestion is obvious. Elsewhere all over 

 the globe there is only one physical cause which determines rocky 

 matter into such ring-like forms as these, and which determines also 

 an included space of depth more or less profound. This physical 

 cause is the eruptive action of volcanic force. When anchored in the 

 central lagoon of a coral atoll, are we not simply anchored in the cra- 

 ter of an extinct volcano — its walls represented by the corals which 

 have grown upon it, its crater represented by the harbor in which our 

 ship is lying ? The vegetation is not difficult to account for. The 

 coral grows until it reaches the surface. It is known to flourish best 

 in the foaming breakers. These, although confronted and in the 

 main resisted by the wondrous tubes and cells, are able here and there 

 in violent storms to break off the weaker or overhanging portions of 

 the coral and dash them in fragments upon the top of the reef. Often 

 the waves are loaded with battering-rams in the shape of immense 

 quantities of drift-timber. These bring with them innumerable seeds 

 and hard nuts able to retain their vitality while traversing leagues of 



