224 APPENDIX. 



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 sub- 

 side, the reefs which grew to the surface during the subsiding 

 movement, would still closely skirt the coast. After some 

 hesitation, I have thought myself justified in leaving these 

 islands coloured blue. 



Mariana Archipelago, or Ladrones. — Guahan : 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 Freycinet's Hydrog* Mem. there 

 is an account of these reefs, and in the atlas, a map on a large 

 scale ; coloured red. — Rota : ' L'ile est presque entierement 

 entouree des recifs ' (p. 212, Freycinet'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 : the N.E. coast, and like- 

 wise the western shores appear to be fringed ; but there is a 

 great, irregular, hornlike 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 exception 

 perhaps of Torres, which resembles in form the madreporitic 

 island of Medinilla), and appear to be without reefs. — Mangs, 

 however, is described (by Freycinet, p. 219, Hydrog.) from 

 some Spanish charts, as formed of small islands placed l au 

 milieu des nombreux recifs; ' and as these reefs in the general 

 chart of the group do not project so much as a mile ; and as 

 there is no appearance from a double line, of the existence of 

 •deep water within, I have ventured, although with much 



