Dr. Nugent on the Geology of the Island of Antigua . 473 
hill, Rat Island, and I think also Constitution hill, gave me the 
idea of its being subordinate to, and partly included in the marl. 
If subordinate, it may have marl above and beneath also ; whatever 
marl is beneath bears no kind of proportion to the superincumbent 
masses, and are thin layers of a few feet thickness. 
With regard to the shells in the marl, you may rest satisfied that 
neither the land shells, nor marine ones, which lie in close associa- 
tion with them, are derived from the surface ; you may find them 
on digging forty feet into the sheer virgin marl, and at considerable 
elevations above the sea. The turbinated helix is the only one 
which is known existing here terrestrial. The lenticular shell 
(Bulimus?) if terrestrial, does not occur so on the island. The 
rugose helix with a contracted lip, from Spanish point, Barbuda, 
which I took out of the marl in company with marine shells, is not 
found recent either there or here. With regard to the singular 
ground pearl, I cannot be so confident, and I speak doubtingly 
in the paper ; I believe it to be derived exclusively from the 
marl, though it may possibly be in some unaccountable manner the 
production of some recent insect on the surface, but I can get 
no rational conjecture concerning it; I certainly believe it to 
be of animal origin, and have no doubt at present that it comes 
from the interior of the marl, and belongs to it like the shells, but 
I have not that strong evidence as in the case of the latter. The 
ground pearl generally has an opening, as if the ovum or larva had 
escaped ; but in a few cases I have found them without opening, 
containing a minute portion of mucous matter ; the negroes then 
call them live ground pearl, but I cannot make out any reason for 
this. It is singular that turkies and other poultry devour these 
ground pearls ; and their death ensues in consequence, unless im- 
mediate relief be afforded ; vinegar is poured down the throat ; 
3 o 2 
