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 entièrement entourée des récifs” (page 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 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 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, page 219, “Hydrog.”) from some Spanish charts, as formed of small islands placed “au milieu des nombreux récifs;” 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 hesitation, to colour them red. Respecting _Folger_ and _Marshall_ Islands which lie some way east of the Marianas, I can find out nothing, excepting that they are probably low. Krusenstern says this of Marshall Island; and Folger Island is written with small letters in D’Urville’s chart; uncoloured.