138 ICE AND GLACIERS. 



to pressure. The compressed snow which I now take out, 

 you will see, has been transformed into a hard, angular, 

 and translucent cylinder of ice ; and how hard it is, 

 appears from the crash which ensues when I throw it to 

 the ground. Just as the loose snow in the glaciers is 

 pressed together to solid ice, so also in many places 

 ready-formed irregular pieces of ice are joined and form 

 clear and compact ice. This is most remarkable at the 

 base of the glacier cascades. These are glacier falls 

 where the upper part of the glacier ends at a steep rocky 

 wall, and blocks of ice shoot down as avalanches over the 

 edge of this wall. The heap of shattered blocks of ice 

 which accumulate become joined at the foot of the rock- 

 wall to a compact, dense mass, which then continues its 

 way downwards as glacier. More frequent than such cas- 

 cades, where the glacier-stream is quite dissevered, are 

 places where the base of the valley has a steeper slope, 

 as, for instance, the places in the Mer de Glace (Fig. 14), 

 at g, of the Cascade of the Glacier du Geant, and at i and 

 h of the great terminal cascade of the Glacier des Bois. 

 The ice splits there into thousands of banks and cliffs, 

 which then recombine towards the bottom of the steeper 

 slope and form a coherent mass. 



This also we may imitate in our ice-mould. Instead of 

 the snow I take irregular pieces of ice, press them to- 

 gether ; add new pieces of ice, press them again, and so 

 on, until the mould is full. When the mass is taken 

 out it forms a compact coherent cylinder of tolerably clear 

 ice, which has a perfectly sharp edge, and is an accurate 

 copy of the mould. 



This experiment, which was first made by Tyndall, shows 

 that a block of ice may be pressed into any mould just 

 like a piece of wax. It might, perhaps, be thought that 

 such a block had, by the pressure in the interior, been 

 first reduced to powder so fine that it readily penetrated 



