90 Couthouy on Coral Formations 



a sort of steep talus extending to the next below it ; and al- 

 lowing for inequalities in the growth of the corals, offers a 

 dead level of from twenty to one hundred and fifty yards 

 broad, terminating for the most part at the fragmentary beach, 

 and often having less than a foot of water upon it at low tide, 

 except in the numerous hollows and gullies. 



It has been suggested that this succession of terraces was 

 owing to the action of the surf, which breaks heaviest, and of 

 course tears off the largest masses, upon the extreme edge of 

 the plateau ; that when this has proceeded so far as to weaken 

 in a measure the force of the rollers, a less powerful surf 

 breaking against the inner wall thus formed, will in time 

 form a second terrace, and then a third, or even a fourth, 

 though this is perhaps rare, before it spreads harmlessly over 

 the broad upper shelf. Yet although the sea acts with great 

 force in abrading the reef, I doubt much whether it can have 

 produced such results as these. It would be more likely to 

 cause a long uniform slope, from the farthest limit of the 

 breakers, to their origin at the margin of the reef. 



It is more in accordance with appearances to suppose that 

 such a slope once really existed, and that the reef subsequent- 

 ly sunk so low as to prevent the growth of the coral on this 

 inclined plane beyond a certain line. There may then have 

 ensued an interval during which the reef was stationary, 

 when the polypes would naturally build upwards from the 

 depth suited to their habits, and in time raise it to its former 

 level, thus forming the lowest wall, while the dead reef be- 

 yond constituted the lowest terrace. A second inclined plane 

 would be produced by the abrasive action of the surf, and a 

 second or third period of sinking, followed by one of rest and 

 re-elevation, would give the outer portion of the reefs that 

 peculiar conformation which they at present exhibit. 



It is upon the lower terraces and margin of the upper one, 

 that the corals are found in their greatest variety, and exhibit 

 the richest hues. Clusters of orange, v?^let, crimson, green 

 of every shade, purple, blue and yellow, -are intermingled in 

 gay confusion, and with a brilliance yet softness of coloratian 

 of which pen or pencil can give but a faint idea. When first 



