Miscellaneous . 487 



barrier reefs surrounding volcanic islands, and passing gradually 

 towards tlie south into coast reefs, which are closely applied to coral 

 reefs elevated to as much as 200 feet. The grouj) of islands termi- 

 nates in a small island entirely destitute of reefs, separated from 

 the rest by a channel four geographical miles in breadth. If we 

 were to apply Darwin's theory to this example, we should have to re- 

 gard this southernmost island as a resting point, whilst the northern 

 • part, by sinking, had rendered the formation of atolls possible. In- 

 dependent of the improbability that a mountain- chain ascending from 

 the deep sea at a distance from all other insular groups, and having 

 so small a horizontal extension (sixty miles in length by six to seven 

 miles in breadth), should possess so great a difference of vertical 

 movement, facts directly observed testify against a depression, 

 nay, even render it probable that an elevation has taken place in 

 recent times. The northern volcanic islands are formed by two dif- 

 ferent basaltic eruptions, one of which bears the present and the 

 older elevated reefs of the south, whilst the second partially overlies 

 them. Traces of a trachytic eruption also occur, but, apparently, 

 isolated from the larger basaltic island. These islands, therefore, 

 belong to a comparatively very recent geological period. And the 

 elevated coral reefs of the south, partly converted into dense coral- 

 line Kmestone, in other places decomposed into chalk, pass directly 

 over into the existing reefs. A depression is farther disproved by the 

 nature of the submarine surface in the interior of the lagoon-chan- 

 nel. Whilst in the north there is a deep and often very broad 

 channel which separates the outer reef from the shore of the island, 

 the numerous small elevated coralline limestone islands of the south 

 are united by a surface extending for many miles nearly horizontally 

 scarcely 4-6 fathoms beneath the surface of the sea, and which, in 

 stiU water at the time of the spring tides, may be traced out of the 

 sea into the supramarine rocks and islands. A horizontal siirface 

 attaining such colossal dimensions could not possibly be formed 

 during a depression which, a few miles further north, had produced 

 a channel of 70 fathoms in depth. 



The author rather regards the physical influences, especially the 

 internal sea-currents caused by the rain, and the exterior direct and 

 diverted ones, as the causes which have produced in the north the 

 atolls, and in the south the coast reefs, simultaneously with an 

 elevation. "Whilst in the latter the deep-going eroding action of the 

 wave-blow or the wash of the sea has gradually planed away the 

 dense and solid coralline limestone to a nearly horizontal surface, 

 which lies at about the depth to which the sea-wash is capable of 

 acting, in the north the becks coming down from the mountains, 

 conjointly with the wash and currents of the sea, have acted much 

 • more strongly upon the uncommonly soft, readily decomposable 

 basalt of the west, than was the case with the limestone in the 

 south, and have eaten out the deep lagoon-channels, which in par- 

 ticular places extend to the width of a mile between the solid 

 ground and the outer reef. — Verhandl. der pliys.-med. GesellscJi. in 

 Wurzburg, February 1, 1868. 



