which exist in snow-fields, and (5) that they persist under very considerable pressure, it is legitimate to assume that a granular crystalline condition persists throughout all stages, and is a feature of progressive growth. [Illustration: +Fig.+ 223.—Figure showing cones of granules of ice which have been washed down the front of the glacier by streamlets, and accumulated after the manner of talus or alluvial cones. North Greenland.] =Inauguration of movement.=—Eventually the increase in depth of snow and ice in a snow-field gives rise to motion. The exact nature of the motion has not yet been demonstrated to the satisfaction of all investigators. Brittle and resistant as ice seems, it exhibits, under proper conditions, some of the outward characteristics of a plastic substance. Thus it may be made to change its form, and may even be moulded into almost any desired shape if carefully subjected to sufficient pressure, steadily applied through long intervals of time.[123] These changes may be brought about without visible fracture, and have been thought to point to a viscous condition of the ice. There is much reason, however, as will be seen later, to question this interpretation of the ultimate nature of the movement. Whatever this may be, the _mass result_ of the movement in a field of ice is comparable, in a superficial way at least, to that which would be brought about if the ice were capable of moving like a viscous liquid, the motion taking place with extreme slowness. This slow motion of ice in an ice-field is _glacier motion_, and ice thus moving is _glacier ice_. [Illustration: +Fig.+ 224.—Ice-caps of small size. The figure also shows some valley glaciers extending out from the main ice-sheet and from the local ice-caps. A portion of the North Greenland coast, north of Inglefield Gulf. Lat. about 78°. (Peary.)] [Illustration: +Fig.+ 225.—Small ice-caps in the northwestern part of Iceland. (Thoraddsen’s geological map of Iceland.)] [Illustration: +Fig.+ 226.—A glacial lobe, midway between an ice-cap and a valley glacier. A protrusion from a local ice-cap east of Cape York, Greenland.]