Obsidian, West Indies, i, 237.

—, used for cutting instruments by the Mexicans, xvi, 161.f

Occultation of Aldebaran, July, 1830, xix, 170.

[Ocean,] natural history of, v, 128.

—, color of, vi, 198; xxix, 237.

—, —, cause of, xvii, 170; xxvi, 65.f

—, depth of, v, 130; xl, 407.

—, —, not determined from the echo, xxxviii, 160.

—, temperature in different parts v, 129; xxv, 130.

—, — and saltness of, at different depths, xxiii, 10.