PACIFIC OCEAN. 
229 
cate 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 pro- 
longed beneath the sea in an extremely steep slope, reefs 
formed there during subsidence will remain closely attached 
to the shore, and will be undistinguisliable from fringing- 
reefs. Now we know that the submarine flanks of most atolls 
are very steep ; and if an atoll after upheaval and before the 
sea had eaten deeply into the land, and had formed a broad 
flat surface, were again to subside, the reefswhicli grewto the 
surface during the subsiding movement, would still closely 
skirt the coast. After some hesitation, I have thought my- 
self justified in leaving these islands coloured blue. 
Mariana Archipelago, or Ladrones. — Gualian : 
almost the whole of this island is fringed by reefs, which 
extend in most parts about a third of a mile from the land. 
Even where the reefs are most extensive, the water within 
them is shallow. In several parts there is a navigable 
channel for boats and canoes within the reefs. In Frey- 
cinet’s Hydrog. Mem. there is an account of these reefs, 
and in the atlas, a map on a large scale ; coloured red.— 
liota : ‘ L’ile est presque entierement entouree de recifs ’ 
(p. 212, Ereycinct’s Hydrog. Mem.). These reefs project 
about a quarter of a mile from the shore ; coloured red. — 
Tinian : the eastern coast is precipitous, and is without reefs ; 
but the western side is fringed like the last island ; coloured 
red. Saypan: theN.E. coast, and likewise the western shores 
appear to be fringed ; but there is a great, irregular, horn- 
like reef projecting far from this side ; coloured red.— 
Farallon de Medinilla appears so regularly and closely 
fringed in Freycinet’s charts, that I have ventured to 
colour it red, although nothing is said about reefs in the 
Hydrographical Memoir. The several islands which form 
the northern part of the group are volcanic (with the excep- 
tion perhaps of Torres, which resembles in form the madre- 
