For, while the cold of a glacial age increased, the saltness of the sea increased also, because of the great amount of fresh water evaporated from the ocean, and stored in ice-sheets on the great continents and islands of the globe. Thus the briny sea was maintained in a liquid state, while washing vast ice-fields and glaciated shores and floating the numerous icebergs of a freezing age. The cold which radiated from such ice-bound seas must have been severe; but meanwhile the evaporation from the ocean was much reduced, while the saltness and coldness of the sea increased, and so prevented the ice of a glacial period from gaining invincible proportions before the independent circulation of the southern ocean was arrested. Therefore, the remaining warmth of the tropical waters after gaining free access to the antarctic latitudes was able to overcome the accumulated cold of that frigid region. At this date the observant navigators who have visited the antarctic seas report that the surface currents above the latitude of Cape Horn, while being drifted eastward by the prevailing westerly winds, also set toward the antarctic ice cliffs, as shown on map No. 2. The reason why this southerly set of the surface currents becomes noticeable above the latitude of 55° south is because the tropical currents which set southward from the torrid latitudes on the western sides of the Atlantic, Indian, and Pacific Oceans, although largely turned away from the high latitudes by the westerly winds and drift currents, are also able to send sufficient water into the great belt of westerly winds to furnish water for the deep under-currents setting northward from the antarctic shores. Thus the surface waters moving from the north in order to gain the higher latitudes, after entering the westerly wind-belt, are moved in drift currents by the impelling winds easterly over many degrees of longitude, and also at the same time slowly southward among the cooling icebergs, because of the attraction caused by the difference of temperature and density between the northern drift waters and the icy seas of the antarctic ice barrier. Consequently, the gradual movement of the surface waters of the westerly wind-belt southward before entering the higher latitudes is not generally apparent; for it is after they enter latitudes where the globe becomes much reduced in circumference that their southern movement in the contracted seas becomes more noticeable. The impact of this southerly current, which finds its outlet in deep under-currents, and retards somewhat the increase of ice on the southern continent at this date, also largely prevents the small icebergs and field-ice from floating northward, away from the antarctic ice barrier; for it is such large icebergs as penetrate the deep under-currents that are the best able to move into the more temperate latitudes.