228 The National Geographic Magazine 



composed of the sedimentary and com- 

 pound type, includes Sombrero, Dog, 

 Anguilla, St Martin, St Bartholomew, 

 Barbuda, Antigua, the Grande-Terre 

 of Guadeloupe, Marie Galante, and 

 Desirade. 



The inner belt facing the Caribbean 

 includes Saba, St Eustatius, St Christo- 

 pher, Nevis, Monserrat, Basse-Terre, 

 Guadeloupe, Dominica, Martinique, St 

 Lucia, St Vincent, the Grenadines and 

 Grenada constituting the newest and 

 highest summits of the Windward group, 

 attaining heights approximating 5,000 

 feet in all the islands mentioned except 

 the two most northern, Saba and St 

 Eustatius, which rise 2,820 and 1,950 

 feet respectively, and the Grenadines. 



GEOLOGY OF THE ISLANDS 



The configuration and structure show 

 that their history extends back to con- 

 siderable antiquity. In the first place, 

 while the primary configuration of all 

 these islands is constructional — largely 

 due to extrusive piling up — the pres- 

 ent minor details of configuration, ex- 

 pressed in steep coastal bluffs, benches, 

 slopes, and canyons, are modified by 

 erosion, which has required consider- 

 able time for development. True crater 

 shapes, except in St Eustatius, Nevis, 

 and St Christopher, are inconspicuous, 

 and are merely secondary summit fea- 

 tures in the other islands, occurring 

 parasitically upon masses of old eroded 

 volcanic debris reaching a height of 

 4,000 feet, which have lost the features 

 of their original contour through ero- 

 sion. Secondly, the islands are all com- 

 posed largely of vast piles of old tuffs 

 and trachytic or andesitic debris of 

 many eruptive epochs, like the volcanic 

 heights of the Costa Rican plateau, 

 which indicate long continuation of the 

 vulcanism since comparatively remote 

 geologic epochs, reaching back most 

 probably to Eocene time. 



This main or interior chain is com- 



posed of piled up volcanic debris, and 

 upon the islands of Guadeloupe, Marti- 

 nique, and St Vincent there have been 

 active volcanic eruptions in historic 

 time, 1797 in the former and 1812 in the 

 latter. Soufrieres, hot springs, etc., 

 show that this activity is only slumber- 

 ing quiescent in nearly all these islands. 

 Besides, most of them still possess upon 

 their summits one or more true craters, 

 while Saba and St Eustatius are com- 

 posed of simple crater cones now qui- 

 escent. While these facts attest recent 

 eruptivity in the islands, there is much 

 evidence presaging the conclusion that 

 the present vulcanism is merely the sur- 

 vival of that which began earlier in 

 geologic history, and that the main mass 

 of the material composing the islands 

 was ejected long before the dawn of 

 human history. 



True elevated reefs — normal, unal- 

 tered reef rocks raised by epeirogenic 

 elevation to heights not exceeding 100 

 feet above the sea — do not occur near 

 sea-level in the Leeward margin of the 

 inner belt of the Caribbee Islands. 



In St Christopher, St Eustatius, Gua- 

 deloupe, Martinique, St Lucia, and Gre- 

 nada disturbed fossiliferousbeds of Ple- 

 istocene or recent age are exceptionall}- 

 found interbedded in volcanic debris of 

 the lower slopes at altitudes of two or 

 three hundred feet above the sea, show- 

 ing that uplifting as well as extrusion 

 has in part produced the present emi- 

 nences, and that vulcanism existed in 

 or prior to Pleistocene time. The fos- 

 sils enumerated are hardly older than 

 Pliocene and are most probably Pleisto- 

 cene, and their border-like position 

 shows that the greater mass of the isl- 

 ands were ejected in previous epochs. 



So much for the main chain of the 

 Caribbees considered by themselves; but 

 the eastern belt, of the compound type, 

 owe their present position above the sea- 

 level to the epeirogenic uplifts which 

 affected the Caribbean area in later geo- 

 logic time. 



