SCIENTIFIC RESULTS 



109 



Berg ice melts slower than the artificial variety and the water 

 obtained from it is fresh and pure. The color of the bergs is 

 a peculiar opaque flat white, often mistaken by the inexperienced for 

 snow, often Avith soft irridescent hues of green and blue. Many 

 bergs are also tinged in places with a brown, yellowish stain, due 

 probably to diatoms and other forms of planktonic life in whicli our 

 northerii seas are so richly abundant. The snowy white appearance 

 is caused by surface weathering of a few inches to a foot or more 

 in depth, and also to the eli'ect of the sun's rays which release in- 

 numerable air bubbles; the ice underneath this surface film is stated 

 to remain a clear deep, green color. If a sample be examined closely 

 it will be seen to be covered with innumerable white threadlike lines 



A Close-up view of Iceberg ice 



Figure 71. — Tlir< e samples of ieeiierg ice. The two largest pieces of slaty opaque 

 whiteness emphasize the physical character of iceberg ice. a mixture of sublimated 

 snow crystals and air brought together under great pressure. The smallest piece 

 was taken from a vein of clear ice often to be found in many icebergs. The veins 

 are probably old cracks and fissures that have filled with thaw wati r either in the 

 berg itself or when it was a part of the glacier. (Photograph after II. T. Barnes.) 



etched all over the surface. A melting surface on close examination 

 reveals the disarticulation of the individual glacier grains which 

 average about three-sixteenths inch in diameter and which are 

 separated one from another by depressions sometimes one-fourth to 

 one-half inch across. This structure gives the ice a roughened, 

 pebbly surface. Few icebergs are structurally homogeneous through- 

 out, most of them being striped by one or more blue or green veins, 

 or ribbons, of compact, transparent ice which stand out strikingly 

 again.^t the porous-white background. These ranging in width 

 from an inch or more to several feet are formed by crevasses filling 

 the water and then freezing as clear, blue ice while the berg was still 

 a part of the margin of the ice cap. Other blue bands are also pro- 

 duced by the pressure and shearings that the glacier streams expe- 



