STRUCTURE OF THE TURKS ISLANDS 275 



5. The question of the foundations of the aeolian rock is then 

 dealt with, and the reply is that in the Turks Islands the aeolian 

 sandstone passes down into consolidated reef debris, consisting of 

 coarse sand, dead shells, and coral fragments, which have been 

 thrown up on reef rock under the existing conditions of sea-level 

 (pp. 262-4). . 



6. Whilst discussing the modern process of reclamation m the 

 Turks Group, the structure of the islands is treated in detail ; and it 

 is shown that in the case of the larger islands, where lagoons have 

 been usually enclosed during the development of the new land, the 

 mangroves have been an important reclaiming agency (pp. 265-9). 



7. The comparison of old and recent charts of the Turks Islands, 

 and of the Bahamas generally, does not often yield definite results ; 

 but we may quote the conclusion of Alexander Agassiz, who paid 

 considerable attention to the matter, that the configuration of the 

 Bahamas has not been materially changed since their discovery by 

 Columbus, a conclusion that involves the implication that during a 

 period of 400 years no great change has occurred in the relations 

 between land and sea in this region (pp. 264-5). 



8. All the questions raised by the consideration of the Turks 

 Islands are issues raised in connection with the Bahamas as a whole. 

 The original much greater extent of the land of aeolian origin, which 

 is postulated by the author in the case of the Turks Islands, was 

 assumed twenty years ago by A. Agassiz for the whole Bahamian 

 region. Although we cannot assume that in distant ages a con- 

 tinuous land-surface occupied the area of the existing archipelago, 

 it is probable that several of the islands were as large as an average 

 English county and that their maximum elevation did not exceed 

 500 feet. They were completely covered by wind-blown sand, and 

 in fact their entire thickness was the work of the drifting dune, 

 there being little to indicate that there was any covering of vegetation 

 of any extent (pp. 269-270). 



9. The history of the Bahamas is the history of the sand-dune. 

 The original islands must have offered a spectacle not to be found 

 on the same scale in any insular territory in the present era, not 

 even in the great coral-reef regions of the Indian and Pacific Oceans. 

 These unusual formations require unusual conditions, and the author 

 looks for them in the conditions that prevail on the sea-board of a 

 great continent where the dune holds its sway. The conditions of the 

 present in the Bahamian region are confessedly not those of the past ; 

 and in what, we may ask, has been the change (pp. 270-1) ? 



10. Before answering this question, the author describes the sand- 

 wastes on the sea-board of Peru, where the shifting sand-hill reigns 

 supreme, and here he draws in part on his own experiences. He then 

 replies to the query above put, and suggests that just as the cold 

 waters of the Peruvian Current determine the aridity of the sea- 

 boards of North Chile and Peru, so in ancient times a southward 

 extension of the Arctic or Labrador Current would have produced 

 similar effects on the Bahamas (pp. 271-2). 



11. Not to be ignored, however, is the view of the " extensionist " 

 school based on zoological evidence that the Bahamas and the 



