186 BULLETIN: MUSEUM OF COMPARATIVE ZOÖLOGY. 
and Cuba, and probably San Domingo, having been well described 
from the last named island by Gabb. The shell formation underlyimg 
the coastal swamps of Panama, although having a matrix of land debris, 
is also of similar age. 
A. Agassiz has described at length in his chapter on the Florida 
Reefs! the wide extent of somewhat similar formations which constitute 
the small keys and reefs of Florida,? as well as the whole of the eastern 
and western coasts of the southern end of the peninsula. He has also 
shown that a large part of the peninsula of Yucatan is composed of 
similar material. 
These formations are also largely developed around some of the 
Virgin Islands, and the. peculiar island of Barbuda, which the writer 
has recently studied, is composed entirely of similar rock occurring at 
two well marked levels 5 and 125 feet above the sea. 
This material in the Antilles, Virgin. Islands, Yucatan, and Barbuda, 
is characterized by many beautifully preserved Mollusca embedded in 
a white limestone chalky matrix. A small species of Bulla, still living 
in the adjacent waters, is specially abundant, sometimes almost entirely 
composing the mass. 
The true elevated reefs of Jamaica are related to kindred phenomena 
in many parts of the West Indian region. The term reef rock in this 
paper is restricted to those strata which are composed almost entirely 
of compound coral heads of modern reef building genera, such as 
Porites, Siderastrea, Orbicella, Meandrina, and Madrepora, and does 
not include other white limestones not of unmistakable reef origin. 
The genera and species of these elevated reefs, with two exceptions in 
arbados found one each by Gregory and Vaughan, are all the same 
as those of the growing reef of the region today. The living reefs have 
been reconnoitred and described very minutely by A. Agassiz, and he 
has noted the elevated reefs in numerous places along the Central 
American coast, the Tortugas, the Great Antilles, Windward Islands, 
3arbados, and Florida. He has also shown that these reefs were 
formed on shallow submarine banks of less than fifteen fathoms, and 
there can be no doubt but they formed the West Indian region during 
periods of elevation. 
Elevated reefs similar to those of Jamaica are known to border A 
large portion of the island of Cuba. There, as in Jamaica, they occur 
only in benches immediately adjacent to the sea, nowhere a hundred 
1 Three Cruises of the Blake. 2 Ibid., Vol. I. p. 54. 
3 Ibid, Vol. I. p. 62. 
