273 



by slight changes of level. Even the Bahamas may be similar remnants 

 of old volcanic piles.* 



OSCILLATIONS OF THE OCEAN'S BOTTOM 



There has been still a third and less understood process at work in 

 producing the present configuration of the Windward islands. This is 

 the great process of regional movement (uplift and probably subsidence) 

 of the sea bottom, together with all the islands resting thereon — veritable 

 heavings of the bosom of the earth. 



These movements are clearly and unmistakably recorded in the con- 

 figuration of elevated reefs, benches, and terraces already mentioned. 

 By these processes banks which once existed only below the water have 

 been elevated into islands, and islands which showed but slightly above 

 the water have been lifted still higher, and all of the islands, of whatever 

 composition and structure, both volcanic and sedimentary, have partici- 

 pated in these movements. 



Plains and terraces which originated by marine erosion at or below 

 sealevel are now lifted into terraces and island summits, in many cases 

 covered by growths of coral reef or shell debris. Old baselevels of ero- 

 sion, which represented land planed down to sealevel, are now similarly 

 lifted and again undergoing destructive degradation. Colonies of sea 

 life, which inhabited the marginal waters of the ocean at the shore of the 

 volcanic piles, are now found at heights of from 100 to 900 feet above the 

 sea, resting on the great masses of the volcanic piles which have been 

 lifted with them. 



Concerning the elevations, the evidence is sharp and clear, the subsi- 

 dences are only inferential, but nevertheless probable. 



Owing to the slowness of these movements, it is impossible to measure 

 them or to state with positiveness whether they are in operation at pres- 

 ent, but that such is the case may be inferred from the recent character 

 of the upraised benches and the unmistakable records of their long con- 

 tinuity in the past. 



In the writer's work on Jamaica, in part V, " Changes of level in the 

 West Indies," attention is called to the evidence of uplift and subsidence 

 recorded in the Greater Antilles. Darwin and others have long since 

 described similar phenomena on the Pacific coast of South America. 

 Writers have also shown that elevated benches and terraces conspicu- 

 ously mark the periphery of the European Mediterranean. 



* Moreau de Jones, in 1816, discovered that the calcareous outer islands of the Caribbee chain 

 rested on igneous formations. He showed that these islands were mostly situated to the wind- 

 ward of the volcanic group, and that even in the volcanic islands, where calcareous formations 

 were also found, the latter were mostly on the Atlantic side. In fact, there is evidence that the 

 vents of volcanic activity have migrated westward slowly during geologic periods, as the sea 

 planed away the Windward piles. 



