36 THE OCEA]S'. 



In the open sea ice is also formed. In winter, when the air is 

 calm, the snow falls in large flakes on the tranquil waves, the sea is 

 soon covered with a kind of scum, which gradually changes into a 

 thin coating of ice. The wind may break this layer when barely 

 formed, and the tiny scattered fragments may be surrounded with 

 water from the melted snow, which does not mix with the salt-water 

 of the sea, and glitters feebly v/iih iridescent hues beneath the 

 rays of an oblique sun ; but this does not last long, and the cold soon 

 re-forms the layer of ice.* Even in despite of wind and wave, innu- 

 merable needles of ice, which give to the surface of the water a pasty 

 appearance, spread their network over the sea, and soon consolidate 

 into a thick layer, which constantly increases as the cold of winter 

 becomes more and more rigorous. By the natural chemistry of the sea, 

 which is an immense laboratory, the mass of ice is in a great measure 

 freed from the salt which is found in sea- water ; for, according to 

 the observations of Mr. Walker, it contains hardly more than five 

 thousandths ; that is to say, about a fifth of its normal quantity. 

 The water nearest to the new ice mixes with the expelled salt, be- 

 comes heavier, and as the freezing-point is at the same time lowered 

 it descends deeper in the water without becoming solid. This is 

 the reason wh)^ in the open sea the water is rarely frozen for any 

 considerable depth below the surface, as one might expect.f 



In consequence of the frequent collision of these fragments of ice 

 tossed by the waves, they generally assume the same circular form 

 as the flakes of ice on rivers. They are roundlets of a very incon- 

 siderable diameter, slightly raised at the edges ; the English sailors 

 term them " ice-cakes." But the cold becoming more intense, these 

 disks finalty adhere to one another, and before long millions of them, 

 united in vast fields, form islands which stretch to the farthest 

 horizon. Sometimes these "ice-fields" have a superficial extent of 

 hundreds of thousands of square miles, and even constitute, by 

 their dimensions, real continents. Those which border upon the 

 eastern coast of Greenland have not been melted for four centuries, 

 and eflectually prevent the approach of navigators to the land ; 

 those connected with the Siberian coasts are still more considerable, 

 because of the long extent of shore which serves as their base. In 

 the Polar archipelago of America, ice bars the entrances of the 

 channels almost every 3^ear, and raises before the navigator an impass- 



* Gustare Lambert, Expedition ati role Nord. Bulletin de la Societe de Geographic, Dec. 

 1867. 



t Neumann, TIeber die BiclitigTicit heirn Meerwasser. 



