ATOLL LAGOON HAVENS 2O9 



present a more or less complete ring of reefs about their 

 shores. In case such an island should gradually sink, the 

 result would necessarily be the creation of an atoll. 



Lately Dr. Murray and others have contended for the 

 view which explains the formation of an atoll on the sup- 

 position that a coral bank forms at any point on the sea-floor 

 where the depth of water is not too great and where there 

 is a continuous marine current of sufficient temperature to 

 maintain the growth of the reef-building species. The 

 cavity or lagoon within the reef is explained by the solvent 

 action of the water, which tends to take up and to bear 

 away the lini)' material with which it comes in contact. It 

 seems not improbable that these islands with cup-shaped 

 centres may be produced in the v.'ays indicated by both these 

 hypotheses. That advanced by Dr. Murray, however, seems 

 to be the simplest and most rational explanation of the 

 facts. 



From the point of view of the student of harbors it is 

 only necessary to remark that, owing to the small amount 

 of fertile soil which the narrow strip of land enclosing the 

 atoll lagoon affords, these havens can never have much com- 

 mercial importance. 1 hey serve as shelters for a few small 

 trading ships, and they may in time be prized by yachtsmen ; 

 but they can never have much relation to commerce. Though 

 much more striking and beautiful features than the barrier 

 reefs, they are of very much less economic value. Probably 

 far more ships have been cast away upon these coral reefs 

 of mid-ocean than have been protected from storms in the 

 beautiful but generally inaccessible havens which they afford. 

 Thus as a whole we must look to the barrier reefs as affording 



the only really important harbors which are produced through 

 14 



