ON CORAL ISLANDS. 213 



tation; whilst others are overflowed with every return- 

 ing tide. 



It seems to me, that when the animalcules, which 

 form the corals at the bottom of the ocean, cease to live, 

 their structures adhere to each other, by virtue either of 

 the glutinous remains within, or of some property in salt 

 water ; and the interstices being gradually filled up 

 with sand and broken pieces of coral washed by the sea, 

 which also adhere, a mass of rock is at length formed. 

 Future races of these animalcules erect their habitations 

 upon the rishig bank, an8 die in their turn to increase, 

 but principally to elevate, this monument of their won- 

 derful labours. The care taken to work perpendicularly 

 in the early stages, would mark a surprising instinct in 

 these diminutive creatures. Their wall of coral for the 

 most part, in situations where the winds are constant, 

 being arrived at the surface, affords a shelter, to leeward 

 of which their infant colonies' may be safely sent forth ; 

 and to this their instinctive foresight it seems to be owing, 

 that the windward side of a reef exposed to the open sea, 

 is generally, if not always, the highest part, and rises al- 

 most perpendicular, sometimes from the depth of 200, 

 and perhaps many more fathoms. To be constantly co- 

 vered with water, seems necessary to the existence of the 

 animalcules, for they do not work, except in holes upon 

 the reef, beyond low water mark ; but the coral sand and 

 other broken remnants thrown up by the sea, adhere to 

 the rock, and form a solid mass with it, as high as the 

 common tides reach. That elevation surpassed, the fu- 

 ture remnants, being rarely covered, lose their adhesive 

 property ; and remaining in a loose state, form what is 

 usually called a key, upon the top of the reef. The new 

 bank is not long in being visited by sea birds ; salt plants,, 

 take root upon it, and a soil begins to be formed ; a cp- 





