RELATIONSHIP OP THE VOLCANOES OP THE WEST -INDIES. 205 



Since the mid-Tertiary epoch there have been terrestrial 

 oscillations causing the islands to be enlarged somewhat beyond 

 their present size, only to again be depressed to near their 

 present altitude. In several islands at least a slight com- 

 paratively recent elevation is noticeable, as seen by geological 

 evidence, though we have no satisfactory records from an 

 historical standpoint. 



Thus it appears that the volcanic phenomena were closely 

 connected with those of earth movements, which in proportion 

 have declined as also has the volcanic activity. 



While the volcanic forces have built up ridges and cones, by 

 the accumulation of the debris of eruption, yet in part their 

 elevation has been due to upper thrusts of the ridges themselves, 

 fringed with fragments of the sea bottom ; but the great changes 

 of the whole now submerged plateau may in part have been 

 tectonic, but if so they have been modified by what in 

 America is called epeirogenic or slow continental movements ; 

 for every w^here the surfaces of the submarine plateau are 

 dissected by systems of valley-like indentations which have not 

 obscured the movements due to volcanic or other forces. 



The vibrations in the rocks during the recent eruptions were 

 sufficient to break the submarine cables, often overhanging the 

 walls of the submerged canyons. It has also been reported that 

 the sea bottom had collapsed in places. Such sinkings in the 

 crust have been contradicted with the general statement that 

 there have been no apparent changes. If such a collapse of the 

 submarine crust had really occurred, then there might be some 

 doubt as to the origin of part of the valley-like features, made 

 know^n by the dredgings. Although the district is volcanic with 

 caldrons and cul dc sacs of valleys, in part originated by the 

 destructive forces of exploding volcanoes, yet the general 

 features are those of denudation ; so that the idea that the 

 valley forms in the submarine plateau have been due to past 

 atmospheric action, does not seem to be affected. Accordingly, 

 from the records of these drowned valleys, we obtain our 

 knowdedge of great changes of level of land and sea in recent 

 geological times. 



The terrestrial movements, as also the volcanic, have been 

 mostly along the line represented by the chain of islands — the 

 margin of the Atlantic Ocean — which has been marked as a 

 zone of terrestrial weakness favourable to both tectonic move- 

 ments and volcanic action, and suggestive of renewed volcanic 

 activity along this course. But the recent eruptions in 

 Martinique and St. Vincent, those in Central America and 



