256 CORAL AND ATOLLS 



toss up, but are unable to move farther by reason of the waning 

 of their force. In this way the characters of the typical zones 

 of the barrier become developed. 



We have seen that the first part of the barrier will be 

 formed at the windward side of the ring, and here its develop- 

 ment will be always most complete ; the larger masses will 

 be upon its outer border, and its level zone will be far wider 

 than in any other part of the circle. Now, in the case of an 

 atoll that lies in the zone of the Trade winds, this will be a 

 very marked feature of the barrier ; and in the Cocos-Keeling 

 atoll it is particularly striking. 



It will be seen that the very perfection of the windward 

 barrier tends still further to protect the leeward side of the 

 reef; and it does this with such effect that the waves are 

 altogether powerless to bring about the changes that produce 

 barrier formation. Upon the leeward side the boulders are 

 not raised, the breccia platform is not made, and there is no 

 rampart at the level of maximum wave action over which the 

 seas rush. There is, therefore, a leeward gap in the barrier. 



Since the waves are always rolling across the ocean in 

 one direction, it is only their feeble echo that washes against 

 the lee side of an atoll in the Trade wind zone, and so the 

 mariner's maxim, that the entrance to an atoll lagoon is on the 

 lee side of the atolJ, is a very well-founded one. 



It has been said, in the description of the Cocos-Keeling 

 atoll, that the barrier is the pioneer of the dry land, and that 

 wherever the barrier exists it is potentially the site of island 

 formation : a most important stage in atoll formation has 

 therefore been arrived at. With the completion of a portion 

 of the barrier, a turning-point is arrived at in the history of 

 the reef, for now, instead of remaining as a wave-swept circle, 

 it easily becomes a fully developed atoll. The stages of the 

 process are easily seen, in miniature, at any point in an atoll 

 ring ; and the whole process of island building may be studied 

 at any of the inlets between two adjacent islands. Just as the 

 first step in the formation of the barrier consisted of some chance 

 boulder being hurled by storms upon the top of its fellows, so 



