46 GLACIERS 



appearances caused by the cracking and squeezing of the 

 mud flow. 



The squeezing to which glaciers are subject in their 

 downward movement is often gigantic in amount. Glaciers 

 from neighbouring rock valleys unite and form one slowly 

 flowing river of ice without the breadth of the channel 

 being proportionately increased. The glaciers which unite 

 to form the great Gorner glacier above Zermatt have a 

 width of ten miles, and soon after they have joined together 

 the width is reduced to two miles, and farther on to one mile. 

 The depth of the glacier is, of course, increased when its 

 width is diminished. Swiss glaciers have been bored to a 

 depth of 800 feet without reaching the bottom, and, small 

 as they are compared with the great glaciers of the glacial 

 age, it is calculated that they attain in places to a depth 

 of 2000 feet. There is enough solid ice in the great 

 Gorner glacier to build three cities the size of London ! 

 There are about 1500 glaciers in Switzerland, some of 

 which, of course, unite with one another as they descend, 

 and the total area they cover is over looo square miles, 

 with an average thickness difficult to estimate, but pro- 

 bably not over-estimated at 250 feet. 



The colour of ice, like that of water, is blue, and of 

 course the colour is deep and intense in proportion to the 

 thickness of clear ice or water through which the light 

 passes. There is a great deal of persistent error about the 

 blue colour of water. A good many people insist that it 

 is due to the reflected blue colour of the sky. It is easy 

 to prove that this is not so since the clear water of seas 

 and lakes is seen to be blue when the sky is completely 

 overcast. When the water is not very deep and the 

 bottom is white, the colour is a very fine turquoise blue. 

 But if the water is of such great depth that no light is 

 reflected up from the bottom through the water, then the 

 colour is a deep indigo. If the water has any yellow stain 



