Neither water nor wind can do these things.  Indeed, nothing like the drift is being formed by any process now at work anywhere in the eastern United States.  To find the agent which has laid this extensive formation we must go to a region of different climatic conditions.

The inland ice of Greenland.  Greenland is about fifteen hundred miles long and nearly seven hundred miles in greatest width.  With the exception of a narrow fringe of mountainous coast land, it is completely buried beneath a sheet of ice, in shape like a vast white shield, whose convex surface rises to a height of nine thousand feet above the sea.  The few explorers who have crossed the ice cap found it a trackless desert destitute of all life save such lowly forms as the microscopic plant which produces the so-called “red snow.”  On the smooth plain of the interior no rock waste relieves the snow’s dazzling whiteness; no streams of running water are seen; the silence is broken only by howling storm winds and the rustle of the surface snow which they drive before them.  Sounding with long poles, explorers find that below the powdery snow of the latest snowfall lie successive layers of earlier snows, which grow more and more compact downward, and at last have altered to impenetrable ice.  The ice cap formed by the accumulated snows of uncounted centuries may well be more than a mile in depth.  Ice thus formed by the compacting of snow is distinguished when in motion as glacier ice.

The inland ice of Greenland moves.  It flows with imperceptible slowness under its own weight, like, a mass of some viscous or plastic substance, such as pitch or molasses candy, in all directions outward toward the sea.  Near the edge it has so thinned that mountain peaks are laid bare, these islands in the sea of ice being known as NUNATAKS.  Down the valleys of the coastal belt it drains in separate streams of ice, or glaciers.  The largest of these reach the sea at the head of inlets, and are therefore called tide glaciers.  Their fronts stand so deep in sea water that there is visible seldom more than three hundred feet of the wall of ice, which in many glaciers must be two thousand and more feet high.  From the sea walls of tide glaciers great fragments break off and float away as icebergs.  Thus snows which fell in the interior of this northern land, perhaps many thousands of years ago, are carried in the form of icebergs to melt at last in the North Atlantic.

Greenland, then, is being modeled over the vast extent of its interior not by streams of running water, as are regions in warm and humid climates, nor by currents of air, as are deserts to a large extent, but by a sheet of flowing ice.  What the ice sheet is doing in the interior we may infer from a study of the separate glaciers into which it breaks at its edge.