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STRUCTURAL GEOLOGY OF NORTH AMERICA 



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divisions may be recognized if the submarine features are considered. 

 First, on the west is the Aves Rank that ends on the north at its only 

 emergence, Aves Island. It is slightly convex eastward. The next division 

 is the Grenada basin, a broad and not very deep depression, which bounds 

 the island festoon of the typical Caribbees. These islands are Pliocene- 

 Pleistocene volcanic cones, and they form the inner or younger Caribbees. 

 Outside the volcanic arc and at the north are the Limestone Caribbees, 

 another row of islands which seem to merge with the younger volcanic 

 islands. Outside of the Limestone Caribbees is the deep, narrow Brownson 

 trough, which shallows southward and ends in the wide Tobago trough. 

 East of the Tobago trench is the Trinidad-Barbado element that extends 

 northward in the form of the Barbado submarine ridge outside the Puerto 

 Rico trench. 



The volcanic or younger Caribbees begin on the north with Saba ( 2820 

 feet high) and extend in succession through St. Enstatius (1950 feet), St. 

 Christopher (4314 feet), Nevis (3596 feet), Redonda (1000 feet), Mont- 

 serrat (3002 feet), Basse Terre of Guadeloupe (4869 feet), Isles des 

 Saintes (1036 feet), Dominica (4747 feet), Martinique (4428 feet), St. 

 Lucia (3145 feet), St. Vincent (4048 feet), the Grenadines (a series of 

 rocky islands on a narrow bank nearly 100 miles long), and finally 

 Grenada (2749 feet). A considerable number of these islands have well- 

 preserved cones. Some volcanoes are still active, notably La Soufriere 

 on St. Vincent, which erupted violently in 1902 and killed 2000 people, 

 and Mont Pelee on Martinique. 



The Limestone Caribbees are characterized by limestones and pyro- 

 clastics into which various hypabyssal rocks have been intruded; these are 

 overlain by younger marine limestones. To the Limestone Caribbees 

 belong Sombrero, Anguilla, St. Martin, St. Bartholomew ( Barthelemy), 

 Barbuda, Antigua, Grande Terre of Guadeloupe, Desirade, and Marie 

 Galante. Woodring (1928), Senn (1940), and Maxwell (1948) have sum- 

 marized the geological history of this group. 



Fig. 42.8. The Lesser Antilles showing the Limestone Caribbees (also called older and outer) 

 the Volcanic Caribbees (also called younger and inner). 



Outer Limestone Caribbees 



The following summary is principally from a report by Maxwell ( 1948). 

 In the outermost islands of the Limestone Caribbees, Sombrero and 



