GEOLOGY. 7 
drusy crystals of carbonate of lime. The bird is supposed 
to have been the “boatswain” (Phaéton ethereus,) which 
resorts to the islands during the breeding season, and 
makes its nest in the hollows of the cliffs; the bird in 
this case being immured, during the period of incubation, 
by some fresh deposit of sand, which had afterwards 
hardened into the walls of its prison-house. Cases of 
bones and eggs being found, have occurred in other parts 
of the islands, imbedded in the limestone: and what may 
be considered more singular, a gold knee buckle was said 
to have been found not far from the Tanks on the Main 
Island ; and a canister shot was dug up in coarse limestone, 
whilst excavating the foundations for one part of the North 
Bastion, across the bottom of the cavern. Turtle bones 
have also been found in the loose sand of the sea beach ; 
the turtles sharing the same fate as the bird before men- 
tioned, being buried whilst depositing their eggs. Colonel 
Nelson was informed by an eye-witness, that the dimen- 
sions of the skeletons of these animals were nine feet in 
length and seven in breadth. He terminates his list of 
animal organics by stating, that almost every shell known in 
the surrounding sea may be found in the rock quite perfect. 
As regards the Bermuda chalk deposit, Colonel Nelson 
attributes its existence in this locality to the decomposition 
of zoophytes, from the least calcareous to the large and 
massive Meandrina and Astrea. He states that these 
animals, and the many marine plants, consisting chiefly of 
lime, produce this chalk, just as terrestrial animals and 
vegetables give carbon to soil when they decay. 
In various parts of the islands, rudely shaped cylindrical 
blocks are to be found on the surface; and of these well 
