466 0. D. von Engeln — Studies on Ice Structure. 



to the disintegration of rock debris incorporated in the ice. He 

 accounts for the gliding planes of ice crystals, the development 

 of Forel's stripes and of capillary fissures in the ice, on the basis 

 of the presence of such films of salt solution. Elsden* endorses 

 the same idea, quoting Buchanan. 



On slowly melting and evaporating, in the experimental lab- 

 oratory, at air temperatures near and below the freezing point, 

 the ice crystals of the compressed ice cylinders were individu- 

 ally marked out by well-defined grooves. A block of glacier 

 ice (from the Ulecillewaet Glacier, Canada) similarly preserved 

 showed the same phenomenon. Like grooves commonly 

 develop on the surface of cakes of artificial ice slowly melting 

 in refrigerators and if such ice is split with a sharply pointed 

 ice pick it will be found that the mass will commonly break 

 up into prismatic crystals, the grooves marking the surface out- 

 crop of the crystal boundaries. The fact that in ail these cases 

 the grooves have a considerable width, from 1/32 inch to 1/16 

 inch, shows that the volume of the separating films is cpiite 

 appreciable. The fact that these grooves develop on melting 

 slowly in air temperatures near the freezing point indicates 

 that the melting point of the interstitial material is lower than 

 that of the bulk of the granules. It does not follow, however, 

 that the width of the grooves is an index to the thickness of 

 the interstitial films in the interior of the ice, for a very dilute 

 salt solution would be very effective in developing a channel 

 by melting at the surface in contact with air at temperatures 

 above the normal melting point of pure ice. In the interior 

 of the ice the film is probably much thinner and the solution 

 more concentrated than in the outcropping gi'ooves. 



Before the writer knew of the writings of Buchanan and 

 Quincke his attention was called to the possibility of there 

 being different solubilities at the centers and peripheral zones 

 of glacier grains by phenomena attendant upon the melting of 

 icebergs from Alaskan tidal glaciers in sea waters. On the 

 surface of those portions of berg that had been melting below 

 the sea-water surface a unique "hammered silver" effect devel- 

 oped. (See fig. 8.) The centers of each of the polygonal ice 

 grains were hollowed out and these concave depressions met 

 in ridges where the grains came in contact with their neigh- 

 bors. The ice under such surfaces was solid, transparent, clear 

 blue. When, however, such bergs melted in the air (after 

 stranding at low tide) the surfaces became smooth, the ice lost 

 its transparency, the grains became disarticulated, colored solu- 

 tions could be filtered through the intergrain fissures and the 

 surface of the grains became marked with an arborescent sys- 



*Elsden, J. V.: Principles of Chemical Geology, London, 1910, p. 136. 



