The continent of Australia occupies a comparatively small portion of the Pacific, while innumerable islands stud its surface many degrees on either side of the equator, of which a great number are volcanic, showing that its bed has been, and indeed actually is, the theatre of violent igneous eruptions. So great is its depth, that a line five miles long has not reached the bottom in many places; yet as the whole mass of the ocean counts for little in the total amount of terrestrial gravitation, its mean depth is but a small fraction of the radius of the globe. The bed of the Atlantic is a long deep valley, with few mountains, or at least but few that raise their summits as islands above its surface. Its greatest breadth, including the Gulf of Mexico, is 5000 miles, and its superficial extent is about 25 millions of square miles. This sea is exceedingly deep: in 27° 26ʹ S. latitude and 17° 29ʹ W. longitude Sir James Ross found the depth to be 14,550 feet; about 450 miles west from the Cape of Good Hope it was 16,062 feet, or 332 feet more than the height of Mont Blanc; and 900 miles west from St. Helena a line of 27,600 feet did not reach the bottom, a depth which is equal to the height of some of the most elevated peaks of the Himalaya; but there is reason to believe that many parts of the ocean are still deeper. A great part of the German Ocean is only 93 feet deep, though on the Norwegian side, where the coast is bold, the depth is 190 fathoms. Immense sandbanks often project from the land, which rise from great depths to within a few fathoms of the surface. Of these, the Aghullas Banks, off the Cape of Good Hope, are amongst the most remarkable; those of Newfoundland are still greater in extent: they consist of a double sandbank, which is supposed to reach to the north of Scotland. The Dogger Bank, in the North Sea, and many others, are well known. According to Mr. Stevenson, one-fifth of the German Ocean is occupied by sandbanks, whose average height is 78 feet, an area equal to about one-third of Great Britain. Currents are sometimes deflected from their course by sandbanks whose tops do not come within 50 or even 100 feet of the surface. Some on the coast of Norway are surrounded by such deep water that they must be submarine table-lands. All are the resort of fish.