=The outwash plain or apron.=—The water which descends from the glacier surface in the glacier wells or mills, eventually arrives at the bottom, where it follows a sinuous course within a tunnel melted out in the ice. Much of this water may issue at the ice front beneath the coarse rock materials which are found there, and so be discovered with the ear rather than by the eye. The water within the tunnels not flowing with a free surface but being confined as though it were in a pipe, may, however, reach the glacier margin under a hydrostatic pressure sufficient to carry it up rising grades. Inasmuch as it is heavily charged with rock débris and is suddenly checked upon arriving at the front it deposits its burden about the ice margin so as to build up plains of assorted sands and gravels, and over this surface it flows in ever shifting serpentine channels of braided type (Fig. 308). Such plains of glacier outwash are described as _outwash plains_ or _outwash aprons_. Rising as it does under hydrostatic pressure the water issuing at the glacier front may find its way upward in some of the crevasses and so emerge at a level considerably above the glacial floor. It may thus come about that the outwash plain is built up about the nose of the glacier so as partially to bury it from sight. When now the ice front begins a rapid retirement, a depression or _fosse_ (Fig. 309 and Fig. 339, p. 314) is left behind the outwash plain and in front of the moraine which is built up at the next halting place. [Illustration: FIG. 309.—Diagrams to show the manner of formation and the structure of an outwash plain, and the position of the fosse between this and the moraine.] =The continental glacier of Antarctica.=—In Victoria Land, upon the continent of Antarctica, so far as exploration has yet gone, the continental glacier is held back by a rampart of mountains, as has been shown to be true of the inland ice of Greenland. The same flat dome or shield has likewise been found to characterize its upper surface (Fig. 310). The most noteworthy differences between the inland ice masses of Greenland and Antarctica are to be ascribed to the greater severity of the Antarctic climate and to the more ample nourishment of the southern glacier measured by the land area which it has submerged. There is here no marginal land ribbon as in Greenland, but the glacier covers all the land and is, moreover, extended upon the sea as a broad floating terrace—the shelf ice (Fig. 311). This barrier at its margin puts a bar to all further navigation, rising as it does in some cases 280 feet above the sea and descending to even greater depths below (plate 15 B). [Illustration: FIG. 310.—Map showing the inland ice of Victoria Land bordered by the shelf ice of the Great Ross Barrier. The arrows show the direction of the prevailing winds (based on maps by Scott and Shackleton).]