STRUCTURE OF CORAL ISLANDS. 177 



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. On moving these masses, which gener- 

 ally 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 Actinias or living flowers, the spiny echini and 

 sluggish biche-de-mar, while swarms of shells, having a soldier 

 crab for their tenant, walk off with unusual life and stateliness. 

 Moreover, delicate corallines, Ascidise and sponges tint with 

 lively shades of red, green and pink, the under surface of the 

 block of coral which had formed the roof of the little grotto. 



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. They are 

 probably a result of a subterranean movement or shaking. 



The heach consists of coral pebbles or sand, with some 

 worn shells, and occasionally the exuviae 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 arti- 

 ficial wall or embankment running parallel with the shores. 

 On Clermont Tonnerre, the first of these islands visited by us, 

 the natives seen from shipboard, standing spear in hand along 



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