PACIFIC OCEAN. 223 



generally the case, I have little doubt that the reefs of the 

 Pelew islands ought to be ranked in the barrier class, and I 

 have coloured them pale blue. In Lieut. Elmer's chart there 

 is a horse-shoe-formed shoal, 13 miles N.W. of Pelew, 

 with 15 fathoms within the reef, and some dry banks on 

 it ; coloured dark blue. — Spanish, Martires, Sanserot, Pulo 

 Anna and Mariere Islands are not coloured, because I know 

 nothing about them, excepting that according to Krusen stern, 

 the second, third, and fourth mentioned, are low, placed on 

 coral-reefs, and therefore perhaps include a lagoon ; but Pulo 

 Mariere is a little higher. Since the above remarks were 

 written Prof. Semper has published an interesting article 

 (Zeitschr. f. Wissensch. Zoologie. Bd. xiii. 1863, p. 558) on 

 these islands. He states that the southern islands consist of 

 coral-rock, upraised to the height of from 400 to 500 feet ; 

 and some of them, before their upheaval, seem to have existed 

 as atolls. They are now merely fringed by living reefs. The 

 northern islands are volcanic, deeply indented by bays, and 

 are fronted by barrier-reefs. To the north there are three 

 true atolls. Prof. Semper doubts whether the whole group- 

 has subsided, partly from the fact of the southern islands being 

 formed of upraised coral-rock ; but there seems to me no im- 

 probability in their having originally subsided, then having 

 been upraised (probably at the time when the volcanic rocks 

 to the north were erupted), and again having subsided. The 

 existence of atolls and barrier-reefs in close proximity is mani- 

 festly not opposed to my views. On the other hand, the 

 presence of reefs fringing the southern islands is opposed to 

 my views, as such reefs generally indicate that the land has 

 either long remained stationary, or has been upraised. It 

 must, however, be borne in mind (as remarked in our sixth 

 chapter) that when the land is prolonged beneath the sea in 

 an extremely steep slope, reefs formed there during subsidence 

 will remain closely attached to the shore, and will be undis- 

 tinguishable from fringing-reefs. Now we know that the- 



