The Southern Ocean, which makes the circuit of the world along the parallel of 60° S., in length equal to half the circumference of the earth at the equator, may be considered as occupying the space between the Antarctic Circle and the parallel of lat. 40° S. Owing to the limited number of soundings as yet obtained within its limits, we can only form a general idea of the distribution of its depths. The boundary-line of the fortieth parallel, which separates the Southern Ocean from the Pacific, Atlantic, and Indian Oceans, is occupied alternately by areas of depression, with depths ranging from 2,500 to nearly 3,000 fathoms, and by areas of elevation, or submarine plateaus, approaching to within 1,500 fathoms of the sea-surface. With regard to the general distribution of depth in the Southern Ocean, its bottom appears to rise gradually from nearly 3,000 fathoms at the fortieth parallel (with the exception of the intervening plateaus) to little over 1,500 fathoms at the Antarctic Circle. There are also indications of an area of depression of an average depth of 2,000 fathoms, making the circuit of the globe between the parallels of 50° and 60° lat. S. The whole surface of the Southern Ocean is strewn with masses of floating ice, some of them forming islands many miles in extent, and rising from 100 to 300 feet above the level of the sea--an imposing spectacle, but fraught with much danger to the navigator in these regions. It is this central ocean which supplies the masses of cold water that fill up nearly two-thirds of the total depth of the Atlantic, Pacific, and Indian Oceans. We are indebted to Sir James Ross for the first soundings procured within the Antarctic Circle. They are situated in the wide inlet, discovered by that illustrious navigator in the year 1840, which extends along the meridian of New Zealand, and terminates at the foot of Mount Erebus and Mount Terror. These soundings, which are all under 500 fathoms, viewed in combination with the above-mentioned gradual rise of the bottom of the Southern Ocean toward the Antarctic Circle, justify the assumption that the seas included within the latter do not exceed 1,500 fathoms in depth, their average depth probably falling below this estimate. The extensive formation of ice in this region, as well as the numerous indications of land reported by the daring sailors who have penetrated so far south, suggest the hypothesis of the existence, if not of an Antarctic continent, at all events of a considerable extent of land, rising in the mountain ranges and volcanoes of Victoria Land to 10,000 and 15,000 feet above the level of the sea.