140 CORAL AND ATOLLS 



platform of tlie station gives a very true idea of the height 

 to which the islands rise above it. There are other diffe- 

 rences between the windward and the leeward sides of the atoll. 

 At the southern and eastern extremity the maximum of wind 



FiCt. 47. 



The Lagoo\let op Pulu Luar at High Tide. 



effect is seen, and sand covers the surface of the islands in 

 wind-blown ridges of some depth, so that, in places, actual 

 hills, thirty feet high, rise in Pulu Atas. The barrier flats are 

 far wider on the south side of the group, and larger boulders 

 are piled upon them ; the sea beaches are steeper, and are 

 composed of larger fragments ; and lastly, the lagoon itself is 

 far shallower in its southern portion. 



It has been said that the atoll is horseshoe -shaped, and 

 this form is not confined to the whole collection of islands. 



