The "granular" ice which has been obtained is almost opaque (it consists of grains) and resembles 

 firm ice. Still more unique is the shape of the ice formed from snow, which falls on the surface of 

 new ice, constantly damp with brine. 



Thus, in first approximation, on the basis of structure, sea ice can be divided into needle, 

 sponge and granular, while on the basis of deep formation, into surface, deep and bottom ice. 



Needle ice consists of regular hexagonal pyramids with the axes perpendicular to the surface 

 of the sea (oriented crystals). Such ice resembles glass (externally). 



Sponge ice consists of needles, plates and grains (unoriented crystals) intertwined in various 

 directions. 



Granular ice consists of round grains, i. e. , separate crystals round in form, with nonpar- 

 allel axes. Such ice is formed from ice and snow during friction and pressure of ice floes against 

 each other. When the grains are very close together, this ice also resembles glass. 



"Surface ice" is formed at the very surface of the sea from sea water or snow. If it is 

 formed from sea water when the sea is calm, its structure approximates the needle tj^pe, while 

 when the sea is not calm, it resembles the sponge type. 



"Deep ice" is formed at a certain depth below the surface of the sea; its structure is ordin- 

 arily spongy. Bottom ice is formed on objects lying on the bottom; it is a variation of depth ice, 

 and also has a spongy structure. 



A rougher subdivision of ice according to its external appearance (which can be determined 

 visually) is its classification as vitreous and porous, and as stratified, which is a combination of 

 these two types when they undergo change. 



Recently some investigators approached the question of ice structure from the petrographic 

 point of view; in other words, they examined ice as a mineral, and adapted to it the classification 

 established for rocks. Actually, ice forms from water (which is a primary geological substance) in 

 much the same way as, for example, crystalline silicon rocks form from melted liquid magma. 

 Since during its existence ice undergoes many thermodynamic reactions, ice can also be a meta- 

 morphic rock. This view is shared by many. Some classify ice as neptunic (sedimentary) rock. 

 If such analogies are drawn, surface ice should be classified as an igneous rock, while depth ice, 

 which rises to the surface of the sea and for which the surface is the "bottom" should be classified 

 rather as a sedimentary rock. 



LITERATURE: 62, 77. 



Section 41. Initial Forms of Surface Ice 



Small crystals, in the form of ice needles which spread in every direction and which inter- 

 mingle with each other, form on the surface of the sea when it is calm and there is no wind. These 

 primary formations gradually grow larger, fuse together, and form spots of film on the surface of 

 the sea, which in form resemble congealing lard and which are called "lard ice, "or simply "lard. " 

 Lard ice (ordinarily a dark lead color, which differs only slightly from the color of the water during 

 cloudy weather) externally resembles finely ground ice saturated with water. 



96 



