FORMATION OF CORAL REEFS. 159 
and rapid changes of external influences than the 
Condor. Itmay 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 
