122 THEORY OF THE FORMATION Ch. V. 



thinly interspersed with low islands. Lastly, in the 

 Indian Ocean, the archipelago of the Maldivas is 470 

 miles in length, and 60 in breadth ; that of the Lac- 

 cadives is 150 by 100 miles: as there is a low island 

 between these two groups, they may be considered as 

 one group of a thousand miles in length. To this 

 may be added the Chagos group of low islands, 

 situated 280 miles distant, in a line prolonged from 

 the southern extremity of the Maldivas. This group, 

 including the submerged banks, is 170 miles in length 

 and 80 in breath. So striking is the uniformity in 

 direction of these three archipelagoes, all the islands 

 of which are low, that Captain Moresby, in one of his 

 papers, speaks of them as parts of one great chain 

 nearly 1,500 miles long. I am, then, fully justified 

 in repeating that immense spaces both in the 

 Pacific and Indian Oceans, are interspersed with 

 islands, of which none rise above the height to which 

 the waves and winds in an open sea can heap up 

 matter. 



On what foundations, then, have these reefs and 

 islets of coral been constructed ? A foundation must 

 originally have been present beneath each atoll, at 

 that limited depth which is indispensable for the 

 first growth of the reef-building polypifers. A con- 

 jecture will perhaps be hazarded, that the requisite 

 bases may have been afforded by the accumulation of 

 great banks of sediment, which did not quite reach 

 the surface owing to the action of superficial currents, 

 aided possibly by the undulatory movement of the 



