3o W. J. SOLLAS [januaey 



coral " (Hdiopora coerulea) which extend outwards, branching as they 

 go, for a distance of 3 yards or more. Overlapping the reef lies a layer 

 of consolidated coral breccia ; it has suffered much from erosion by the 

 sea, and bounds the inner side of the depression in cliffs 3 or 4 feet in 

 height. A sheet of clear green water covers the swamp at high tide, 

 converting it into a shallow lake, which as the tide falls empties itself 

 through deep holes in the floor into subterranean passages, which freely 

 communicate with the outer sea. The northern end of this depression 

 is closed by coral breccia, and overgrown with mangroves ; but farther 

 on it recommences and extends through the remainder of the island, 

 almost as far as its northernmost extremity, forming a discontinuous 



Fig. 9. — A Raised Pinnacle of Coral. 



narrow trough bordered by steep cliffs. This trough, and the 

 depression to which it belongs, owes its origin in some degree to 

 solution by sea-water. 



We have deviated from our walk across the island to follow the 

 course of its central depression, let us now return and resume our 

 traverse. The blackened fragments of coral, resembling nothing so 

 much as the clinkers of lava which cumber the slopes of Etna, continue 

 seawards, and are loosely piled to form a gently rising ascent ; so 

 loosely piled that they often topple over at a touch, and afford very 

 uncertain or even dangerous foothold. 



Walking circumspectly, therefore, up the slope we soon reach the 

 summit of a long ridge, and find ourselves looking towards the Andes, 

 some thousands of miles away over the broad waters of the Pacific 

 Ocean. We stand on the top of the " storm-beach," the loftiest region 

 of our island, at the imposing altitude of 10 or even 15 feet, according 



