It is merely necessary to assume that the gravity of the accumulated mass is sufficient to produce the minute temporary liquefaction at the points of greatest stress, the result being accomplished not so much by the lowering of the melting-point as by the development of heat by pressure. [Illustration: +Fig.+ 292.—Portion of the east face of Bowdoin glacier, North Greenland, showing oblique upward thrust, with shear.] This conception of glacial “flowage” involves only the _momentary liquefaction of minute portions of the mass_, while the ice as a whole remains rigid, as its crystalline nature requires. Instead of assigning a slow viscous fluidity like that of asphalt to the _whole_ mass, which seems inconsistent with its crystalline character, it assigns a free fluidity to a succession of particles that form only a minute fraction of the whole at any instant. This conception is consistent with the retention of the granular condition of the ice, with the heterogeneous (in the main) orientation of the crystals, with the rigidity and brittleness of the ice, and with its strictly crystalline character, a character which a viscous liquid does not possess however much its high viscosity may make it resemble a rigid body. =Accumulated motion in the terminal part of a glacier.=—However slight the relative motion of one granule on its neighbor, the granules in any part of a glacier partake in the accumulated motion of all parts nearer the source, and hence all are thrust forward. Herein appears to lie the distinctive nature of glacial movement. Each part of a stream of water feels the hydrostatic pressure of neighboring parts (theoretically equal in _all_ directions) and the momentum of motion, but not the rigid thrust of the mass behind. Lava streams are good types of viscous fluids flowing in masses comparable to those of glaciers and on similar slopes, and, in their last stages, at similar rates, but their special modes of flow and their effects on the sides and bottoms of their paths are radically different from those of glaciers. Forceful abrasion, and particularly the rigid holding of imbedded stones while they score and groove the rock beneath, is unknown in lava streams and is scarcely conceivable. There is, so far as we know, no experimental or natural evidence that any typical viscous body in flowing over a rugose bottom detaches and picks up fragments and holds them as graving tools in its base so fixedly as to cut deep, long, straight grooves in the hard bottom over which it flows. It would seem that competency to do this peculiar class of work, which is distinctive of glaciers, should be demonstrated before the viscous theory of glacial movement is accepted as even a good working hypothesis. Somewhat in contrast with viscous movement, it is conceived that a glacier is thrust forward rigidly by internal elongation, shears forcibly over its sides and bottoms, and leaves its distinctive marks upon them.