18G bulletin: museum of comparative zoology. 



and Cuba, and probably San Domingo, having been well described 

 from the last named island by Gabb. The shell formation underlying 

 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, Slderastroea, Orhicella, 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 

 Barbados 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, 

 Barbados, 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. Tliere, as in Jamaica, the}^ occur 

 only in benches immediately adjacent to the sea, nowhere a hundred 



i Three Cruises of the Blake. 2 ibid., Vol. I. p. 54. 



8 Ibid., Vol. I. p. 62. 



