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- 
eareous 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 Rey. 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 
which nothing like a cell can be detected.” 
Beechey, in his description of Henderson Island, another 
