=Icebergs and snowbergs and the manner of their birth.=—Greenland reveals in the character of its valleys the marks of a large subsidence of the continent—the serpentine inlets or fjords by which its coast is so deeply indented. Into the heads of these fjords the tongues from the inland ice descend generally to the sea level and below. The glacier ice is thus directly attacked by the waves as well as melted in the water, so that it terminates in the fjords in great cliffs of ice (Fig. 317). It is also believed to extend beneath the water surface as a long toe resting upon the bottom (Fig. 319). ┌───────────────────────────────────────────────────────────────────┐ │ PLATE 15. │ │ │ │ [Illustration: _A._ An Antarctic ice foot with boat party landing │ │ (after R. F. Scott).] │ │ │ │ [Illustration: _B._ A near view of the front of the Great Ross │ │ Barrier, Antarctica (after R. F. Scott).] │ └───────────────────────────────────────────────────────────────────┘ [Illustration: FIG. 318.—A Greenlandic iceberg after a long journey in warm latitudes.] The exposed cliff is notched and undercut by the waves in the same manner as a rock cliff, and the upper portions override the lower so that at frequent intervals small masses of ice from this front separate on crevasses, and toppling over, fall into the water with picturesque splashes. Such small bergs, whose birth may be often seen at the cliff front of both the Greenland and Alaskan glaciers, have little in common with those great floating islands of ice that are drifted by the winds until, wasted to a fraction only of their former proportions, they reach the lanes of transatlantic travel and become a serious menace to navigation (Fig. 318). [Illustration: FIG. 319.—Diagram showing one way in which northern icebergs may be born from the glacier tongue (after Russell).] Northern icebergs of large dimensions are born either by the lifting of a separated portion of the extended glacier toe lying upon the bottom of the fjord, or else they separate bodily from the cliff itself, apparently where it reaches water sufficiently deep to float it. In either case the buoyancy of the sea water plays a large rôle in its separation. If derived from the submerged glacier toe (Fig. 319), a loud noise is heard before any change is visible, and an instant later the great mass of ice rises out of the water some distance away from the cliff, lifting as it does so a great volume of water which pours off on all sides in thundering cascades and exposes at last a berg of the deepest sapphire blue. The commotion produced in the fjord is prodigious, and a vessel in close proximity is placed in jeopardy.