94 THE FAIRY-LAND OF SCIENCE. 
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 
drawn up from the tropics float on the wide sea, and 
melting in its warm currents, topple over and over* 
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 com- 
panions, from whom it was parted for a time, does 
* 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. 
