SCIENTIFIC RESULTS 



109 



Bei'of ice melts slower than the aitificial variety and the water 

 obtained from it is fresh and pure. The color of the ber<.>;s is 

 a peculiar opa(iue flat white, often mistaken by the inexperienced for 

 snow, often with soft irridescent hues of jzreen and blue. Many 

 beru's are also tinged in places with a bi'own. yellowish stain, due 

 pi()bal)ly to diatoms and other forms of planktonic life in whicli our 

 northern seas are so richly abundant. The snowy white appearance 

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

 in de])th, and also to the effect 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 



FiGUHE 71. — Tlin e samples of iceberg ice. Tlie two largest pieces of slaty opaque 

 whiteness emphasize the ph.vsical 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 H. T. Barnes.) 



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

 ^reveals the disarticulation of the intHvidual glacier grains which 

 average about three-sixteenths inch in diameter and which are 

 'sejiarated one from another by depressions sometimes one-fourth to 

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

 l)ebbly 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 

 lagainst 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- 



