The work accomplished by glaciers is distinctive, for while like rivers, they abrade the valleys through which they pass, carry forward the material which they remove from the surface, and wear, grind, and ultimately deposit it, and while their work therefore includes erosion, transportation, and deposition, their method is peculiar. =Getting load.=—If the surface on which the snow-field which is to become a glacier accumulates be rough and covered with abundant rock débris, as such surfaces usually are, the glacier already has a basal load when its movement begins, for the snow covers, surrounds, and includes such loose blocks of rock as project above the general surface and envelops all projecting points of rock within its field. When the snow becomes ice and the ice begins to move, it carries forward the loose rock already imbedded in it, and tears off the weak points of the enveloped rock-projections. It may perhaps also move some of the soil and mantle rock of the original surface to which it is frozen. In addition to the _subglacial_ load which the glacier thus has at the outset, there may be a surface load which has fallen on the snow or ice from cliffs above. This is especially true of mountain-valley glaciers. If this has been buried by snow and ice it is _englacial_; if it lies on the surface it is _superglacial_. Once in movement, the ice carries away the débris to which it was originally attached, and at the same time gathers new load from the same area. The new load is acquired partly by the rasping effect of the rock-shod ice on its bed, and partly by its rending power which, under favorable circumstances, may quarry out considerable blocks of rock. This “plucking” process is at its best where the ice passes over cliffs of jointed rock or steep-sloped hills.