184 CORALS AND CORAL ISLANDS. 



Beach formations of coral sand-rock are common on the 

 coral islands, and they present the same features in every re- 

 spect as those described. They were observed among the Pau- 

 motus, on Paraka, Honden, Kawehe, and other islands. The 

 stratified character is always distinct, and the layers slope to- 

 ward the water at the usual small angle, amounting to 5-7 

 degrees bordering the lagoon, and 6-8 degrees on the seashore 

 side of the land. Agassiz gives the same angle for the sea- 

 ward slope of similar deposits at Key West. The rock is 

 largely a fine oolite. They often occupy a breadth of thirty 

 to fifty yards, appearing like a series of outcrops ; yet they are 

 frequently covered by the sands of the steep part of the beach. 

 It is probable that they generally underlie the loose surface 

 material of the land. The rock is a fine or coarse sand-rock, 

 or an oolite, or a coral pudding-stone, and consists of beach 

 materials. Occasionally it is quite compact, and resembles 

 common limestone, excepting in its whiter color ; but gener- 

 ally its sand origin is very apparent. On the northern atolls 

 of the Maldives, the beach sand-rock is said to be quarried 

 out in square blocks and used for building. 



In borings by Lieutenant Johnson, of the Wilkes Explor- 

 ing Expedition, on Aratica or CarlshofTs Island, in the Pau- 

 motus, ten or eleven feet were passed through easily, and then 

 there was a sudden transition from this softer rock (probably 

 the beach sand-rock), to the solid reef-rock. 



The drift sand-rock was not met with by the author on any of 

 the coral islands visited. The time for exploration on these 

 islands allowed by the Expedition was too short for thorough 

 work. It has been stated that the more exposed points toward 

 the trades, especially the northeastern and southwestern, are 

 commonly a little higher than other parts ; and it is altogether 

 probable that some of the sand heaps there formed will prove 



