Essay, Gc. 185 
from the analogy of similar caverns in. other. 
parts of che Island, in which they are formed al- 
mos: exclusively in calcareous rock ; and it will 
be necessary, consequently, to modify a remark 
made in the first part ofthe mineralogical essay. 
In regard to the particular economy of this bird, 
his food, and the manner of constructing the 
Edible Nests, as weil assubstance which furnishes 
the matcials, much remains still to be as- 
certained. 
The peninsula which here projects to the 
south beyond the common range of the coast in 
this part, consists of several successive ridges 
running parrallel, almost directly north and south, 
and terminating precipitously at the Oceaij. 
At the extremity they are divided by numerous 
clefts or fissures, which penetrate into the body 
of the bills, and in many instances extend, with 
various windings, to a considerable distance. 
Their direction in general is vertical, the ` hori- 
zontal diameter being the smallest, and they 
are closed above by the same mineral substance: 
which forms the body of the hill Many of these 
fissuresare in contact With the Ocean, the water 
of which occupies the lower portions: in these 
cases. the external openings have remained 
complete, while in more. inland. situations, the 
hills of which we may analogically suppose to. 
cleft i # the me manner, “the. apertures have 
been closed b mposing vegetables or mi: 
ncrals, and ki Fauta to which they lead are 
coricealed. 
. The apertures of those caverns which are at 
he present period. most productive in Bird's 
ests, are situated at the bottom of precipices. - 
whose perpendicular height is between 5o and. 
the 
: too fathoms: they are narrow, and have 
