The Ice-Front in the Inlet. 27 



700 square miles. Most of the precipitation which falls on this 

 area flows off as water in the subgiacial streams; the rest, com- 

 pressed into ice, is forced througli the narrow gateway 22 miles 

 wide into the inlet, where the glacier terminates in a vertical wall 

 of ice varying from 130 to 210 feet above the water surface, from 

 which large masses are continually separating to become icebergs 

 (see page 48 and plates 1, 2 and 13). As already stated, the depth 

 of the water is in places 720 feet ; and as this is not enough to 

 float a mass of ice rising so high above the water as Islmx glacier, 

 the ice must reach to the very bottom and must attain a thick- 

 ]iess of 900 feet. The actual length of the ice-front facing the 

 water is 9,200 feet, or If miles. 



On each side the glacier sends forward a wing, which rises in 

 the shape of a wedge over the stratified sands and gravels of the 

 shore.* The upper surfaces of the wings, like the ice-front, are 

 about 200 feet above the water level. This applies only to the 

 parts of the wings overlooking the inlet ; the parts nearer the 

 side mountains are •'jO to 100 feet lower ; and here the ice ends 

 like an ordinary alpine glacier. The wings are fringed by 

 treacherous ciuicksands, which support large stones and look 

 firm enough ; but the tourist who steps upon them carelessly 

 will quickly sink in over his ankles. These quicksands are com- 

 posed of fine glacial mud, thoroughly soaked with water from 

 the melting ice. 



The ice-front has a wonderful coloring. Places from which ice 

 has recently broken off' are deep blue, sometimes almost Iflack. 

 This color lightens under exposure to the air and sun, and in a 

 few days becomes pure white. All stages are represented in the 

 ice-front, which therefore shows all shades of blue in striking 

 variety. The blue color of the ice is caused by the absorption 

 of the other constituents of the light passing through it, and is 

 exactl}^ analogous to the hues of colored glasses. When exposed 

 to the sun and rain the ice undergoes a kind of weathering near 

 its surface, which prevents the blue light within from passing- 

 out and reflects nearly all of the light which falls on it from out- 

 side; so that we then see merely ordinary white light reflected, 

 practically unchanged, from the ice. 



*Mr Gushing has published (op. cit., pi. iii) a reproduction of a pho- 

 tograph showing the glacier riding on the these gravels. 



">— Nat. (iv.mi. Map,., vol. IV, 1802. 



