April, 1864.—The Royal Standard came in collision with an iceberg 600 feet in height.
Dec., 1856.—Four large icebergs, one of them 700 feet high, and another 500 feet, were met with in lat. 50° 14′ S., long. 42° 54′ E.
Dec. 25th, 1861.—The Queen of Nations fell in with an iceberg in lat. 53° 45′ S., long. 170° 0′ W., 720 feet high.
Dec., 1856.—Captain P. Wakem, ship Ellen Radford, found, in lat. 52° 31′ S., long. 43° 43′ W., two large icebergs, one at least 800 feet high.
Mr. Towson states that one of our most celebrated and talented naval surveyors informed him that he had seen icebergs in the southern regions 800 feet high.
March 23rd, 1855.—The Agneta passed an iceberg in lat. 53° 14′ S., long. 14° 41′ E., 960 feet in height.
Aug. 16th, 1840.—The Dutch ship, General Baron von Geen, passed an iceberg 1,000 feet high in lat. 37° 32′ S., long. 14° 10′ E.
May 15th, 1859.—The Roseworth found in lat. 53° 40′ S., long. 123° 17′ W., an iceberg as large as “Tristan d’Acunha.”
In the regions where most of these icebergs were met with, the mean density of the sea is about 1·0256. The density of ice is ·92. The density of icebergs to that of the sea is therefore as 1 to 1·115; consequently every foot of ice above water indicates 8·7 feet below water. It therefore follows that those icebergs 400 feet high had 3,480 feet under water,—3,880 feet would consequently be the total thickness of the ice. The icebergs which were 500 feet high would be 4,850 feet thick, those 600 feet high would have a total thickness of 5,820 feet, and those 700 feet high would be no less than 6,790 feet thick, which is more than a mile and a quarter. The iceberg 960 feet high, sighted by the Agneta, would be actually 9,312 feet thick, which is upwards of a mile and three-quarters.
Although the mass of an iceberg below water compared to that above may be taken to be about 8·7 to 1, yet it would not be always safe to conclude that the thickness of the ice below water bears the same proportion to its height above. If the berg, for example, be much broader at its base than at its top, the thickness of the ice below water would bear a less proportion to the height above water than as 8·7 to 1. But a berg such as that recorded by Captain Clark, 500 feet high and three miles long, must have had only 1/8·7 of its total thickness above water. The same remark applies also to the one seen by Captain Smithers, which was 580 feet high, and so large that it was taken for an island. This berg must have been 5,628 feet in thickness. The enormous berg which came in collision with the Royal Standard must have been 5,820 feet thick. It is not stated what length the icebergs 730, 960, and 1,000 feet high respectively were; but supposing that we make considerable allowance for the possibility that the proportionate thickness of ice below water to that above may have been less than as 8·7 to 1, still we can hardly avoid the conclusion that the icebergs were considerably above a mile in thickness. But if there are icebergs above a mile in thickness, then there must be land-ice somewhere on the southern hemisphere of that thickness. In short, the great antarctic ice-cap must in some places be over a mile in thickness at its edge.