A Study in the Natural History of Ice 303 



with his pick could one perceive bunches of white ice where 

 the blow of the pick had produced dislocation of the grains. 

 It was only at places on the wall from which the entrance of 

 the grotto was directly visible, that the beginning of the 

 secondary production of white ice could be perceived. 



As the result of my observations in the artificial grotto, 

 I have arrived at the view that the discontinuities which are 

 the characteristic of white ice may perhaps not be entirely absent 

 in the interior of the glacier, because the ice is translucent, but 

 that the white ice which is due to them is certainly not present 

 in such proportion as to permit of its forming with the primary 

 blue ice a ribbon-structure extending throughout the mass of tlie 

 glacier. 



T/ie Case of a Glacier wJiich has never been 

 Exposed to Light. 



Let us imagine that we have a glacier which has always 

 existed in complete darkness. Were it possible to illuminate 

 it for a moment it would appear as an intensely blue moun- 

 tain. If the illumination were continued, the deep blue colour 

 would quickly fade and before very long would be replaced 

 by dazzling whiteness. Viewed in section the glacier would 

 then appear as a blue internal mass contained in a white 

 external wrapper. Indeed this is exactly the appearance 

 which any of the existing glaciers would present if cut in two. 

 An upper and lateral superficial layer, one to two metres 

 thick, of white ice covering a mass of solid blue ice ; it is the 

 condition of equilibrium of a glacier on the surface of the 

 earth. We cannot detect this when we merely look at a 

 glacier from the outside. // is only by penetrating into the 

 inside of the glacier that we become aware that white ice is a 

 secondary feature characteristic of tiie surface. 



While quarrying the ice of a glacier fresh surfaces are 

 continually being exposed, which, in proportion as they are 

 exposed to the daylight, begin to change their colour from 

 blue to white. It might be thought that we are thereby placed 

 on the horns of the dilemma, if we wish to see if there is 

 white ice in the inside of the glacier we must illuminate the 



