April, 1836. AREAS of alternate movements. 565 



ments of those who have visited them, as well as from an 

 examination of the charts, that lagoon islands are not found 

 there. This in itself is remarkable, but it becomes far more 

 so when it is known, that according to all accounts (and 

 distinctly stated by Mr. De la Beche*) they are likewise ab- 

 sent in the West Indian sea, where coral is most abundant : 

 now every one is aware of the numerous proofs of recent 

 elevation in most parts of that archipelago. Again, Ehren- 

 berg has observed that lagoon islands do not occur in the 

 Red Sea : in LyelPs Geology, and in the Geographical Jour- 

 nal, proofs are given of recent elevation on the shores of a 

 large part of that sea. Excepting on the theory of the form 

 of reefs being determined by the kind of movement to which 

 they have been subjected ; it is a most anomalous circum- 

 stance, and which has never been attempted to be solved, that 

 the lagoon structure being universal and considered as cha- 

 racteristic in certain parts of the ocean, should be entirely 

 absent in others of equal extent. 



I may here also just recal to mind the cases of skirting 

 reefs mentioned by M. Quoy (to which number several others 

 might be added), where proofs of elevation occurred. Some 

 general law must determine the marked difference between 

 reefs merely skirting the shore, and others rising from a deep 

 ocean in the form of distant rings. We have endeavoured to 

 show that with a subsiding movement, the first and simple 

 class must necessarily pass into the second, and more re- 

 markable structure. 



To proceed with our examination : to the westward of the 

 prolongation of the line of subsidence, of which Keeling 

 Island is the index, we have an area of elevation. For on 

 the northern end of Ceylon and on the eastern shores of 

 India, elevated shells and corals, such as now exist in the 

 neighbouring sea, have been observed. Again in the middle 

 of the Indian ocean, the Laccadive, Maldive, and Chagos 

 line of atolls or lagoons show a line of subsidence. The 



* Geological Manual, p. 141. 



