CORAL-REEFS. 159 



and elevation having preceded the subsidence of the blue 

 spots : and in this case the juxtaposition of reefs belonging 

 to the two great types of structure is little surprising. We 

 may, therefore, conclude that the proximity in the same 

 areas of the two classes of reefs, which owe their origin to 

 the subsidence of the earth's crust, and their separation 

 from those formed during its stationary or uprising con- 

 dition, holds good to the full extent, which might have 

 been anticipated by our theory. 



As groups of atolls have originated in the upward growth, 

 at each fresh sinking of the land, of those reefs which 

 primarily fringed the shores of one great island, or of 

 several smaller ones ; so we might expect that these rings 

 of coral-rock, like so many rude outline charts, will still 

 retain some traces of the general form, or at least general 

 range, of the land, 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 three principal groups are directed 

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

 S. Pacific ranges in this same direction ; namely, N. Western 

 Australia, New Caledonia, the northern half of New Zea- 

 land, the New Hebrides, Saloman, Navigator, Society, 

 Marquesas, and Austral archipelagoes : in the Northern 

 Pacific, the Caroline atolls abut against the N.W. line of 

 the Marshall atolls, much in the same manner as the 

 E. and W. line of islands from Ceram to New Britain do 

 on New Ireland : in the Indian Ocean the Laccadive and 

 Maldiva atolls extend nearly parallel to the western and 

 mountainous coast of India. In most respects, there is a 

 perfect resemblance with ordinary islands in the grouping 

 of atolls and in their form : thus the outline of all the 

 larger groups is elongated ; and the greater number of the 



