262 VOYAGE TO THE 



CHAP. 

 VIII. 



of the craters, and it be admitted that the lithophy tes 

 are unable to exist at greater depths than those 

 1826.' above-mentioned, we shall have examples of craters 

 of considerably larger dimensions, and more com- 

 plete in their outline, than any that are known upon 

 the land, which, if true, is a curious fact. Until the 

 voyage of the Blossom, it was not generally known 

 that the lagoons in these islands were of such depths, 

 or that the wall of coral which encircles them was 

 so narrow and perfect, as in almost every instance it 

 has been found ; nor that the islands were of such 

 dimensions, as they were designated groups, or chains 

 of islands, in consequence of the wall being broken 

 by channels into the lagoon ; but on examination, 

 the chain is found continuous under water ; and as 

 in all probability it will in time reach the surface 

 and become dry, the whole group may be considered 

 as one island. 



In the plans which I have delivered into the Ad- 

 miralty, the figure and extent of thirty coral islands, 

 out of the many which exist in the Pacific, are care- 

 fully delineated, and a reference to them will more 

 fully explain their nature than any description I 

 can give here. One of these plans * being of par- 

 ticular interest, I have inserted it in the present 

 work, as it exhibits, not only the coral chain en- 

 closing the lagoon, which is the common character of 

 the coral islands ; but, also, an example of several 

 volcanic islands rising within it ; and likewise the 

 peculiarity of the inequality in the sides of the chain 

 mentioned in page 189. 



The subject of the formation of these islands is 



* See the plan of Gambier groupe. 



