194 CORALS AND CORAL ISLANDS. 



Palisades on the Hudson. This appearance of a vertical 

 structure was afterward traced to vertical furrowings by the 

 waters dripping down its front, and the consequent formation 

 of stalagmitic incrustations. Deep caverns were also seen. 



The cliff, though vertical in some parts, is roughly sloping 

 in others, and on the west side, the surface of the island grad- 

 ually declines to the sea. 



The rock is a white and solid limestone, seldom presenting 

 any traces of its coral origin. In some few layers there were 

 disseminated corals, looking like imbedded fossils, along with 

 beautiful casts of shells ; but for the most part it was as com- 

 pact as any ancient limestone, and as uniform in texture. Oc- 

 casionally there were disseminated spots of crystallized calcite. 



The caverns contain coarse stalactites, some of which are 

 six feet in diameter ; and interesting specimens were obtained 

 containing recent land shells that had been enclosed by a cal- 

 careous film while hibernating. 



It is probable that more extensive caverns would have 

 been found had there been more than a few hours for the ex- 

 amination of the island. The Rev. Mr. Williams, in his work 

 on Missionary Enterprises in the Pacific, gives very interesting 

 descriptions of caverns in the elevated coral rock of Atiu, 

 one of the Hervey Group. In one, he wandered two hours, 

 without finding a termination to its windings, passing through 

 chambers with " fretwork ceilings of stalagmite and stalactite 

 columns, which, 'mid the darkness, sparkled brilliantly with 

 the reflected torch-light*" This author remarks, " that while 

 the madrepores, the brain and every other species of coral are 

 full of little cells, these islands (including those resembling 

 Atiu), appear to be solid masses of compact limestone, in 

 ivhich nothing like a cell can be detected" 



Beechey, in his description of Henderson Island, another 



