200 



J. W. SPENCER^ M.A.^ OlSl THE GEOLOGICAL 



throughout the whole chain of islands, there is nothing except- 

 ing the volcanic basement that can be assigned to greater 

 antiquity than that of the early Tertiary days. 



The Windward Islands are practically divided into two 

 parallel chains. The inner one commencing with Saba, continues 

 through St. Eustatius, St. Kitts, Nevis, and Montserrat; the 

 western of the twin islands of Guadeloupe, Dominica, Marti- 

 nique, St. Lucia, St. Vincent, Grenada and the Grenadines, is 

 characterized by complex volcanic formations surmounted by 

 volcanic cones and ridges. The outer chain from St. Croix, St. 

 Martin, Anguilla, Antigua, Barbuda, Grand Terre of Guadeloupe, 

 Marie Galante, to Barbados, with probably some sunken islands 

 between the two last mentioned, is characterized by more or 

 less calcareous formations resting upon the denuded surfaces of 

 an old volcanic foundation. Some of tliese islands are in part 

 mountainous, but of no great elevation, showing the erosion 

 features of considerable antiquity. They are also marked by the 

 rolling outlines of coastal plains, which extend beyond their 

 present shores, and form the summit of the adjacent portions of 

 the submerged plateaus. While the coastal plains, traversed 

 by erosion features, do not prevail upon the western chain of 

 the islands, yet in the large Saba banks, just south-west of the 

 volcanic island of the name, we find the same features repeated 

 at a depth of only 100 feet, or a little more, below the surface 

 of the sea. All these calcareous formations show themselves to 

 be only remnants of such, extending over an immense land area 

 now dismembered and sunken beneath the sea level ; and the 

 apparent gap in their succession between the Guadeloupe 

 Archipelago and Barbados, is represented by three banks of 

 similar form where, it is reasonable to suppose, they are of the 

 same character, and that they are the slightly drowned 

 remnants of the submerged Antillean plateau. 



In the outer chain of islands, we find that the volcanic 

 basement is covered by formations of the older Tertiary era, the 

 upper portions belonging to the Oligocene system, while the 

 lower beds may perhaps reach down to the base of the Eocene. 

 This gives us the clue to the age of the older volcanic forma- 

 tions. These rocks, without describing them accurately, are 

 a sort of dolerite consisting of triclinic felspars with but little 

 magnesium silicate. It is a kind of intermediate eruptive rock, 

 which if found in Paleozoic strata would be called porphorite, 

 and if in the Tertiary, andecite. There is nothing to establish 

 the age of these old rocks beyond the fact that they are below 

 the old Tertiary formation. Such volcanic deposits dissected by 



