Ch. VI. DISTRIBUTION OF CORAL-REEFS. 165 



extent which might have been anticipated by our 

 theory. 



As atolls have been formed during the sinking of 

 the land by the upward growth of the reefs which pri- 

 marily fringed the shores of ordinary islands ; so we 

 might expect that these rings of coral, like so many 

 rude outline charts, would still retain traces of the 

 general form, or at least of the general range, of the 

 islands round which they were first modelled. That this 

 is the case with the atolls in the Southern Pacific, as 

 far as their range is concerned, seems highly probable, 

 when we observe that the principal groups are directed 

 in nearly N.W. and S.E. lines, and that nearly all the 

 mountainous islands and shores in the S. Pacific range 

 in this same direction ; namely, N. Eastern Australia, 

 New Caledonia, the northern half of New Zealand, the 

 New Hebrides, Saloman, Navigator, Society, Marquesas. 

 and Austral archipelagoes. In the Northern Pacific, the 

 Caroline atolls almost abut against the N.W. line of 

 the Marshall atolls, much in the same manner as the E 

 and W. line of islands extending from Ceram to New 

 Britain abuts against New Ireland. In the Indian 

 Ocean the Laccadive and Maldiva atolls extend nearly 

 parallel to the western mountains of India. There is 

 also a close resemblance between atolls and ordinary 

 islands in the manner in which they are grouped, as 

 well as in their shapes. Thus the outline of all the 

 larger groups of atolls is elongated; and the atolls 

 themselves are generally elongated in the same direc- 

 tion with the group. The Chagos group is less elon- 



