On Coral Reefs and Islands. ' S57 
; try? 
Arr. XLI.—On Coral Reefs and Islands.; by Janes D. Dina.— 
Part L. He * 
From the Report on Geology of the Exploring Expedition under Capt. Wilkes, U.S.N. 
1. Genera Features or Corat Reers anp IsLanps. 
Tne general features of reefs and coral islands have often been 
delineated by travellers, and are probably almost as familiar to the 
reader as the scenes of the land around us. Yet a few brief re- 
marks on this point form a necessary introduction to the more 
minute descriptions of structure which follow. 
_ Coral reefs—A wide platform of rock covered with the sea 
except at low tide, borders most of the high islands of the Pacific. 
It is a vast accumulation of coral, based upon the bottom in the 
shallow waters of the shores. ‘This bank or table of coral rock, 
_ Some instances, a grove o 
miles, where the action of the sea has raised the coral structure 
above the waves. ie. 
Se 
The sketch annexed conveys some idea of the peculiar features . . 
. presented by a Pacific island and its encircling reefs, though in 
} order 'to fill out the scene, the jagged heights and deep gorges of 
the islands should be covered with forests and the shores with 
‘groves.and native villages. ‘The coral platform which borders the 
Re ae . f mn ) 
fee + 
