188 bulletin: museum of comparative zoology. 



In Antigua and Porto Rico there is a reef rock entirely dififerent in 

 mode of occurrence, assemblage of species, and lithologic character from 

 the class of modern elevated reefs we have just described, and belongs to 

 an older geologic period, — probably the Miocene or early Pliocene 

 Tertiary. Furthermore, it is evident that these older Antiguan reefs 

 were elevated by orogenic or volcanic uplifts at a period prior to the 

 later epeirogenic elevation of the true modern reefs described. 



True elevated reefs — normal unaltered reef rocks raised by epeirogenic 

 elevation to heights not exceeding 100 feet above the sea — do not oc- 

 cur near sea level in the leeward margin of the Caribbee Islands. The 

 main or inner chain of these islands is in general a mass of volcanic 

 debris almost void of sedimentary rocks. In St. Kitts,^ St. Eustatius,^ 

 Martinique, Dominica,^ and Granada,* ''reef rock^' is alleged to be 

 found tilted at high angles interbedded with volcanic debris, and occur- 

 ring as high as 500 feet above the sea, but we are not able to state 

 whether these are identical with the true elevated reefs. 



On the Central American and Panama (western) coasts of the Carib- 

 be£tn Sea, the modern elevated reefs also occur sparsely at Colon and 

 Limon,^ but not so highly elevated as in the region adjacent to the 

 Windward Passage, standing hardly five feet above the level of the sea. 

 The same may be said of the elevated reefs of Southern Florida and 

 adjacent regions described by Agassiz,^ where heights of eight feet are 

 recorded. 



In the island of Barbados, which geologically belongs neither to the 

 Caribbee nor Antillean type, the modern elevated reefs attain their 

 highest and most perfect development, and rise to exceptional altitudes 

 of over 1,100 feet above sea level or 1,000 feet higher than elsewhere 

 known. This dome-shaped island is composed of a nucleal mass of 

 rocks allied to the Richmond and Montpelier formations, which are 

 covered by a veneering of true reef rock nowhere exceeding one hun- 

 dred feet in thickness, which extends to the very summit of the island, 

 and presents numerous benches and terraces, — the old surfaces and 

 escarpments of the reefs which have been elevated without local de- 



1 Geology of the Northeastern West Indian Islands, 1871, Stockholm, p. 21. 



2 Maclure, Jour. Acad. Nat. Sci. Phila., Vol. I. Part I. p. 147. 

 8 Cleve, loc. cit., p. 45. 



* Harrison, " The Rocks and Soils of Granada," London, 1897, reports beds 

 of coral sand and mud 150 feet above the sea at extreme north end of the island. 



^ Three Cruises of the Blake, Vol. I. 



6 The Elevated Reefs of Florida, Bull. Mus. Comp. Zool., Vol. XXVIII. No. 2, 

 189G. 



