ANTIQUITY OF THE VOLCANOES 267 



existed for countless millions of years during which these volcanoes have 

 been active, evidence of their presence is conspicuously absent from the 

 geological structure. 



ANTIQUITY OF THE VOLCANOES AS ATTESTED BY THE AGE OF THE ROCK 



MATERIAL 



All the evidence indicates that the present vulcanism is the contin- 

 uation of that which began early in geologic history, and that the main 

 mass of the material composing the island was ejected long before the 

 dawn of human history. 



The configuration and the structure of the islands show that their 

 volcanic history extends, at least, as far back as Eocene time, if not Cre- 

 taceous. In Jamaica, Haiti, and Porto Rico, as well as throughout the 

 Virgin islands, the basement formations of the islands (of Cretaceous 

 and Eocene age) are volcanic hornblende-andesite tuffs exactly similar 

 to those now being erupted from Pele. Furthermore, while the primary 

 configuration of all these islands is constructional — largely due to ex- 

 tensive piling- up — the present minor details of configuration, expressed 

 in steep coastal bluffs, benches, slopes, and canyons, are modified by 

 erosion, which has required considerable time for development. The 

 crater shapes are usually secondary summit features located on larger, 

 older, eroded volcanic piles, which have lost the features of their orig- 

 inal contour through erosion. The newly built-up crater at Pele" is an 

 excellent illustration of this fact. The grand Soufriere of Guadeloupe 

 is another. 



A direct proof of the antiquity of this vulcanism is also shown in the 

 tuffs of Antigua, which are very old, as they are overlapped by sup- 

 posedly Eocene sediments. Pervis* has shown that these tuffs are 

 identical in lithologic composition to the ejecta from the volcanoes of 

 Guadeloupe in the present century. 



In Guadeloupe we have also much physiographic evidence concerning 

 the antiquity of the volcanic action. This island is composed of two 

 parts, of about equal area, separated by a shallow creek or strait, Riviere 

 Salee. The most western of these islands (Guadeloupe proper) is a 

 typical volcanic pile of the main Caribbee chain and is thoroughly 

 mountainous. The eastern area (Grande Terre) is an elevated con- 

 structional plain, composed of calcareous sediments of Pleistocene age, 

 overlying a platform of planed-off volcanic tuffs, etcetera. 



The whole geological history of the Caribbean volcanic island is illus- 

 trated by this beautiful map (made by the French) of the double island 

 of Guadeloupe (see plate 44). The island is composed of two great 



* Geology of Antigua. 

 XXXVI— Bull. C4eol. Soc. Am., Vol. 10, 1904 



