The warming of the air has, however, had the effect of damping as it were, the engine stroke, and, as the process is continued, to start a reverse or upward current within the chimney of the anticyclone. The blizzard is thus suddenly ended in a precipitation of the snow, which by changing the latent heat of condensation to sensible heat tends to increase this counter current. [Illustration: FIG. 313.—Snow deltas about the margins of the Fan glacier outlet of Greenland (after Chamberlin).] =The glacier broom.=—During the calm which succeeds to the blizzard, heat is once more abstracted from the surface air layer, and a new outwardly directed engine stroke is begun. The tempest which later develops acts as a gigantic centrifugal broom which sweeps out to the margins of the glacier all portions of the latest snowfall which have not become firmly attached to the ice surface. The sweepings piled up about the margin of continental glaciers have been described as fringing glaciers, or the glacial fringe. The northern coast of Greenland and Grant Land are bordered by a fringe of this nature (plate 14 A, and Fig. 315, p. 288). It is by the operation of the glacier broom that the inland ice is given its characteristic shield-like shape (Fig. 312). The granular nature of the snow carried by the wind is well brought out by the little snow deltas about the margins of Greenland ice tongues (Fig. 313). Obviously because of the presence of the vigorous anticyclone, no snows such as nourish mountain glaciers can be precipitated upon continental glaciers except within a narrow marginal zone, and, as shown by Nansen rock dust from the coastland ribbon and from the nunataks of Greenland, is carried by a few miles inside the western margin, and not at all within the eastern. [Illustration: FIG. 314.—Sea ice of the Arctic region in lat. 80° 5´ N. and long. 2° 52´ E. (after Duc d’Orleans).] =Field and pack ice.=—Within polar regions the surface of the sea freezes during the long winter season, the product being known as _sea-ice_ or _field-ice_ (Fig. 314). This ice cover may reach a thickness by direct freezing of eight or more feet, and by breaking up and being crowded above and below neighboring fragments may increase to a considerably greater thickness. Ice thus crowded together and more or less crushed is described as _pack ice_ or _the pack_.