FORMATION OF CORAL KEEFS. 159 



and rapid changes of external influences than the 

 Condor. It may be seen feeding on the sea-shore 

 under a burning tropical sun, and then, rising 

 from its repast, it floats up among the highest 

 summits of the Andes, and is lost to sight beyond 

 them, miles above the line of perpetual snow, 

 where the temperature must be lower than that 

 of the Arctics. But even the Condor, sweeping 

 at one flight from tropic heat to arctic cold, 

 although it passes through greater changes of 

 temperature, does not undergo such changes of 

 pressure as a fish that rises from a depth of sixty- 

 four feet to the surface of the sea ; for the former 

 remains within the air that surrounds our globe, 

 and therefore the increase or diminution of press- 

 ure to which it is subjected must be confined 

 within the limits of one atmosphere ; while the 

 latter, at a depth of sixty-four feet, is under a 

 weight equal to that of three such atmospheres, 

 which is reduced to one when it reaches the sea- 

 level. The change is proportionally greater for 

 those fishes that come from a depth of several 

 hundred feet. These laws of limitation in space 

 explain many facts in the growth of Coral Reefs 

 that would be otherwise inexplicable, and which I 

 now will endeavor to make clear to my readers. 



For a long time it was supposed that the Reef- 

 Builders inhabited very deep waters, for they were 

 sometimes brought up on sounding-lines from a 



