But if the vapour travels on till it reaches high mountains in cooler lands, such as the Alps of Switzerland; or is carried to the poles and to such countries as Greenland or the Antarctic Continent, then it will come down as snow, forming immense snow-fields.  And here a curious change takes place in it.  If you make an ordinary snowball and work it firmly together, it becomes very hard, and if you then press it forcibly into a mould you can turn it into transparent ice.  And in the same way the snow which falls in Greenland and on the high mountains of Switzerland becomes very firmly pressed together, as it slides down into the valleys.  It is like a crowd of people passing from a broad thoroughfare into a narrow street.  As the valley grows narrower and narrower the great mass of snow in front cannot move down quickly, while more and more is piled up by the snowfall behind, and the crowd and crush grow denser and denser.  In this way the snow is pressed together till the air that was hidden in its crystals, and which gave it its beautiful whiteness, is all pressed out, and the snow-crystals themselves are squeezed into one solid mass of pure, transparent ice.

Then we have what is called a “glacier,” or river of ice, and this solid river comes creeping down till, in Greenland, it reaches the edge of the sea.  There it is pushed over the brink of the land, and large pieces snap off, and we have “icebergs.”  These icebergs — made, remember, of the same water which was first draw up from the tropics — float on the wide sea, and melting in its warm currents, topple over and over* (A floating iceberg must have about eight times as much ice under the water as it has above, and therefore, when the lower part melts in a warm current, the iceberg loses its balance and tilts over, so as to rearrange itself round the centre of gravity.) till they disappear and mix with the water, to be carried back again to the warm ocean from which they first started.  In Switzerland the glaciers cannot reach the sea, but they move down into the valleys till they come to a warmer region, and there the end of the glacier melts, and flows away in a stream.  The Rhone and many other rivers are fed by the glaciers of the Alps; and as these rivers flow into the sea, our drop of water again finds its way back to its home.

But when it joins itself in this way to its companions, from whom it was parted for a time, does it come back clear and transparent as it left them?  From the iceberg it does indeed return pure and clear; for the fairy Crystallization will have no impurities, not even salt, in her ice-crystals, and so as they melt they give back nothing but pure water to the sea.  Yet even icebergs bring down earth and stones frozen into the bottom of the ice, and so they feed the sea with mud.