Various separated parts of the body of Captain Arkwright, who had been lost in 1866 upon the névé of the same glacier, reappeared at its foot after entombment in the ice for a period of thirty-one years. To-day the time of reappearance of portions of the bodies of persons lost upon Mont Blanc is rather accurately predicted, so that friends repair to Chamonix to await the giving up of its victims by the Glacier des Bossons.
Fig. 420.—Lateral and medial moraines of the Mer de glace and its tributary ice streams.
The moraines.—The horns and comb ridges which rise above the glacier surface are continually subject to frost weathering, and from time to time drop their separated fragments upon the glacier. Falling as these do from considerable heights, they reach the ice under a high velocity, and rebounding, sometimes travel well out upon its surface before coming to a temporary rest. Upon a fresh snow surface of the névé their tracks may sometimes be followed with the eye for considerable distances, and their fall is a constant menace to Alpine climbers. Below the névé the larger number of such fragments remain near the cliff, and the lines of flow of the ice within the glacier surface are such that blocks which reach points farther out upon the glacier are later gathered in beneath the cliff at the side ([Fig. 419]). The ridge of angular rock débris which thus forms at the side of the glacier is called a lateral moraine (see [Fig. 411], [p. 385], and [Fig. 420]).
At the junction of two glacier streams, the lateral moraines are joined, and there move out upon the ice surface of the resultant glacier as a medial moraine. Thus from the number of medial moraines upon a glacier surface it is possible to say that the important tributary glaciers number one more ([Fig. 420]).
Fig. 421.—Ideal cross-section of a mountain glacier to show the position of moraines and other peculiarities characteristic of the surface of the bed.
The plucking and abrading processes in operation beneath the glacier, quarry the rock upon its bed, and after shaping and smoothing the separated rock fragments, these are incorporated within the lower layers of the ice as englacial rock débris. In spaces favorable for its accumulation, a portion of this material, together with much finer débris and rock flour, is left behind as a ground moraine upon the bed of the glacier (see [Fig. 421]).