RELATIONSHIP OF THE VOLCANOES OF THE WEST INDIES. 199 



While the Virgin group and the adjacent small islands on the 

 same submerged plateau with Puerto Eico, the Lesser Antilles, 

 or Windward Islands may be considered as commencing with 

 St. Croix* (on the south-eastern side of the great trough across 

 the submarine plateau), and following the form of a crescent for 

 a distance of 750 miles to the coast of South America, this 

 physical barrier between the Caribbean Sea and the Atlantic 

 Ocean, having a breadth of scarcely more than 100 miles, or 

 reduced again to a width of 25 miles, is a submerged plateau dis- 

 membered into the various drowned table-lands, more or less 

 surmounted by mountain ridges and volcanoes, now forming 

 the Windward Islands. Everywhere we find wonderful valley- 

 like land forms indenting the submerged plateau connecting 

 North and South America together. The depressions in the 

 plateau between the islands do not exceed depths of more than 

 2,000 or 3,500 feet below sea level. In one place only is this 

 amount exceeded between the two continents where it is 

 dissected to a depth of 6,000 feet, namely, in the trough between 

 St. Croix and the Virgin Islands, between which and the 

 continent, by way of Puerto Eico and some of the Bahama 

 Islands, an emergence of 2,100 feet would make a continuous 

 land connection. Among the island masses, we find submarine 

 canyons or gorges with a corresponding depth of 6,000 feet, a 

 broad depression between the Grenadines and P>arbados reach- 

 ing to from 6,000 to 9,000 feet, and elsewhere among the Bahamas 

 there are other submarine valleys of depths of more than 12,000 

 feet. All these are reproductions of land features of plateau 

 regions, such as those of Mexico and Central America, so much 

 so that they may be regarded as evidence of the former eleva- 

 tion of the region, forming^ a brido'e between Xorth and South 

 America, across which we now know some animals migrated in 

 the early Pleistocene period. 



The primary foundation of this barrier between the Caribbean 

 and Atlantic basins has never been discovered, but it is 

 probable that no geological formation or physical feature older 

 than some part of the Cretaceous period will ever be found. 

 Except possibly some of the volcanic formations, there is only 

 very little information concerning any rocks as old as this 

 period. In St. Croix and St. Thomas, Cleve found some 

 evidence of the existence of the Cretaceous formation in that 

 region. Possibly the " Scotland Sands " of Barbados, apparently 

 older than the Tertiary era, may also be Cretaceous. Elsewhere 



^ St. Croix (Fr.), Sta. Cruz (Span,) 



O 



