The division between the _névé_ and the glacier proper is not always easily determined. The beginnings of the glacial movement--that is, of the movement of the ice-stream flowing out of the _névé_-field--are somewhat like the beginnings of the movement of the water from a great lake into its outlet. The _névé_ is the reservoir from which the glacier gets both its supply of ice and the impulse which gives it its first movement. There can not be a glacier without a _névé_-field, as there can not be a river without a drainage basin. But there may be a _névé_-field without a glacier--that is, a basin may be partially filled with snow which never melts completely away, while the equilibrium of forces is such that the ice barely reaches to the outlet from which the tongue-like projection (to which the name glacier would be applied) fails to emerge only because of the lack of material. [Illustration: Fig. 2.--Illustrates the formation of veined structure by pressure at the junction of two branches.] A glacier is characterised by both _veins_ and _fissures_. The veins give it a banded or stratified appearance, blue alternating with lighter-coloured portions of ice. As these bands are not arranged with any apparent uniformity in the glacier, their explanation has given rise to much discussion. Sometimes the veins are horizontal, sometimes vertical, and at other times at an angle with the line of motion. On close investigation, however, it is found that the veins are always at right angles to the line of greatest pressure. This leads to the conclusion that pressure is the cause of the banded structure. The blue strata in the ice are those from which the particles of air have been expelled by pressure; the lighter portions are those in which the particles are less thoroughly compacted. Snow is but pulverized ice, and differs in colour from the compact mass for the same reason that almost all rocks and minerals change their colour when ground into a powder. [Illustration: Figs. 3, 4.--Illustrate the formation of marginal fissures and veins.] [Illustration: Fig. 5.--_c_, _c_, show fissures and seracs where the glacier moves down the steeper portion of its incline; _s_, _s_, show the vertical structure produced by pressure on the gentler slopes.]