Special casks were for experimental purposes fastened in the ice to the north of Behring Strait by Melville and Bryant, and two of these were afterwards recovered, the one near the North Cape in northern Norway, and the other in northeastern Iceland (see map, Fig. 315). Peary’s trips northward in 1906 and 1909 from the vicinity of Smith Sound have indicated that between the Pole and the shores of Greenland and Grant Land the drift is throughout to the eastward, corresponding to the westerly wind. Upon this border the great area of Arctic drift ice is in contact with great continental glaciers bordered by a glacier fringe. Admiral Peary has shown that instead of consisting of frozen sea ice, the pack is here made up of great floes from 20 to 100 feet in thickness and that these have been derived from the glacier fringe. Whenever the blizzards blow off the inland ice from the south, leads are opened at the margin of the fringe and may carry strips from the latter northward across the lead. With favorable conditions these leads may be closed by thick sea ice so that with the occurrence of counter winds from the north they do not entirely return to their original position. A continuance of this process may have resulted in the heavy floe ice to the northward of Greenland, which, acting as an obstruction, may have forced the thinner drift ice to keep on the European side of the Arctic pack. [Illustration: FIG. 316.—The shelf ice of Coats Land with the surrounding pack ice showing in the foreground (after Bruce).] About the Antarctic continent there is a broad girdle of pack ice which, while more indolent in its movements than the Arctic pack, has been shown by the expeditions of the _Belgica_ and the _Pourquoi-Pas_ to possess the same kind of shifting movements. In the southern spring this pack floats northward and is to a large extent broken up and melted on reaching lower latitudes. [Illustration: FIG. 317.—Tidewater cliff at the front of a glacier tongue from which icebergs are born.] =The Antarctic shelf ice.=—It has been already pointed out that the inland ice of Antarctica is in part at least surrounded by a thick snow and ice terrace floating upon the sea and rising to heights of more than 150 feet above it (plate 15 B and Fig. 316). The visible portions of this shelf-ice are of stratified compact snow, and the areas which have thus far been studied are found in bays from which dislodgment is less easily effected. The origin of the shelf ice is believed to be a sea-ice which because not easily detached at the time of the spring “break-up” is thickened in succeeding seasons chiefly by the deposition of precipitated and drifted snow upon its surface, so that it is bowed down under the weight and sunk to greater and greater depths in the water. To some extent, also, it is fed upon its inner margin by overflow of glacier ice from the inland ice masses.