It is believed on good grounds of inference, but absolutely without positive evidence, that the south pole is covered with a great cap of ice, and some physiographers have gone so far as to assert its thickness as possibly six miles at the centre. But as to the ice of the north pole, thanks to the efforts to discover a north-west passage which showed us the breach in the wall of the polar fortress, we know very much more.
Sir Edward Belcher encountered ice 106 feet thick drifting into and grounding on the shores of Wellington Channel. It was in Banks Strait that Sir Edward Parry was finally stopped by the great undulating floes, reaching 102 feet in thickness, that he tells us he had never seen in Baffin's Sea or in the land-locked channels the had left behind him, but which filled the whole sea before him. Such floes are the edge of a pack which we may conjecture extends uninterruptedly from shore to shore of the Polar Sea.
IV. Icebergs
Icebergs are masses of ice rising to a great height above the level of the sea, presenting a singular variety in form and appearance. They are masses broken off from glaciers, or from barrier lines of ice-cliff, and owe their origin to the circumstance of glaciers being in a continual state of progress. Glaciers reach the sea shore in many places in the Arctic regions. When pushed forward into deep water, vast masses are lifted up by their inherent buoyancy, and, broken off at the landward end, are borne away by the winds, or on tides and currents, to parts of the sea far removed from their place of formation. Owing to the expansion of water when freezing, and the difference in density between salt and fresh water, the usual relative density of sea water to an iceberg is as 1 to 91674, and hence the volume of ice below water is about nine times that above the surface. The largest icebergs are met with in the Southern Ocean; several have been ascertained to be from 800 to 1000 feet in height, and the largest are nearly three miles long. One was met with 20 deg. south of the Cape of Good Hope, between Marion and Bouvet Isles, which was 960 feet high, and therefore more than 9000 feet, or 1-3/4 mile in thickness.
TABLE OF CONTENTS.
VOL. XII.
Dedication to Sir Robert Cecil
I. The most ancient voyage and discouery of the West Indies performed by
Madoc, Anno 1170. taken out of the history of Wales, &c.
II. The verses of Meredith the sonne of Rhesus making mention of Madoc
III. The offer of the discouery of the West Indies by Christoper Columbus
to K. Henry the 7. February the 13. Anno 1488; with the Kings
acceptance of the said offer