28 ON CORAL REEFS AND ISLANDS. 



Shore platform and emerged land. — The shore platform is 

 from one to three hundred feet in width, and has the general fea- 

 tures of a half-submerged outer reef. Its peculiarities arise solely 

 from the accumulations which have changed the reef into an 

 island. Much of it is commonly bare at low tide, though there 

 are places where it is always covered with a few inches or a foot 

 of water ; and the elevated edge, the only part exposed, often 

 seems like an embankment preventing the water from running 

 off. The tides, as they rise, cover it with water throughout, and 

 bear over it coral fragments and sand, comminuted shells and 

 other animal remains, to add them to the beach. The heavier 

 seas transport larger fragments ; and at the foot of the beach 

 there is often a deposit of blocks of coral or coral rock, a cubic 

 foot or so in size, which low tide commonly leaves standing in a 

 few inches of water.f 



Besides the deep channels cutting into the margin of the reef 

 and giving it a broken outline, there are in some instances long 

 fissures intersecting its surface. On Aratica, (Carlshoff,) and 

 Ahii, (Peacock Island,) they extended along for a fourth to half 

 a mile, generally running nearly parallel with the shore, and at 

 top were from a fourth to half an inch wide. These fissures are 

 not essential features of the reef, and will come up for consider- 

 ation on a future page of this work. 



The beach usually slopes at an angle of 35 to 45 degrees, and 

 consists of coral pebbles or sand, with some worn shells, and oc- 

 casionally the exuvias of crabs and bones of fishes. Owing to 

 its whiteness, and the contrast it affords to the massy verdure 

 above, it is a remarkable feature in the distant view of these 

 islands, and often seemed like an artificial wall or embankment 

 running parallel with the shores. On Clermont Tonnerre, the 

 first of these islands visited by us, the natives seen from ship- 

 board, standing spear in hand along the top of the beach, were 

 believed by some to be keeping patrol on the ramparts of a kind 

 of fortification. This deception arose from the dazzling white- 

 ness of the coral sand, in consequence of which, the slope of the 

 beach was not distinguished in so distant a view. 



The emerged land beyond the beach, in its earliest stage when 

 barely raised above the tides, appears like a vast field of ruins. 

 Angular masses of coral rock, varying in dimensions from one to 

 a hundred cubic feet, lie piled together in the utmost confusion ; 

 and they are so blackened by exposure, or from incrusting lich- 



•}• On moving these masses, which generally rest on their projecting angles and have 

 an open space beneath, the waters at once become alive with fish, shrimps, and crabs, 

 escaping from their disturbed shelter ; and beneath, appear various Actinae or living 

 ilowers, the spiny echini and sluggish biche-la-mar, while swarms of shells having a 

 soldier crab for their tenant walk off with unusual life and stateliness. Moreover, del- 

 icate corallines, Ascidiae and sponges tint with lively shades of red, green, and pink, 

 the under surface of the block of coral wluch had formed the roof of the little grotto. 



