A Study in the Natural History of Ice 3 1 1 



caused by the thoroughness of the disintegration of the ice 

 exposed to the full light of day is a dominant feature of 

 the ice within a distance of a couple of metres from the 

 external surface of the glacier, but also that the leakiness 

 of the ice-wall ceases almost abruptly at this distance from 

 the entrance, so that, except in the immediate vicinity of 

 lamps, or where the ice has been exposed to recent me- 

 chanical disturbance, the walls of the grotto are practically 

 water-tight. 



When the surface of primary ice exposed to the daylight 

 has been obtained by clearing away the rough white ice 

 from an area of the upper surface of the glacier, the trans- 

 formations which have just been described take place very 

 quickly. 



The arched surface of the glacier facilitates drainage, and 

 the melting of the ice on the granular surfaces enlarges the 

 interstices between the grains, so that through them the water 

 escapes as soon as it is produced. In the course of a day or 

 two, according to the intensity of insolation, the compact 

 layer of blue primary ice becomes converted into a discon- 

 nected, easily crumbling layer of white ice, which is not 

 distinguishable from that of the undisturbed surface of the 

 glacier. Consequently the white ice which forms the outside 

 layer of every glacier is a secondary formation, and is derived 

 from the primary blue ice of the interior by the process of sun- 

 weathering, that z's, by disintegration under the influence of solar 

 radiation. 



As the discontinuities which produce white ice are de- 

 pendent on solar action, it is unlikely that they can be present 

 in the interior of the glacier in such proportion as to permit 

 of their forming with the primary blue ice a ribbon-structure 

 throughout the mass of the glacier, as is frequently postulated. 

 This is borne out by the observations made during a series of 

 years in the interior of the Morteratsch Glacier. 



If the water of the intergranular spaces, which is present 

 in the primary ice in so small a quantity compared with the 

 mass of the ice which contains it, is able, by absorbing the 



