THE DENSITY AND VOLUME-WEIGHT OF SOILS, ug 



capillary water, or otherwise flocculated or cemented. Freez- 

 ing of the soil is therefore of material assistance in disintegrat- 

 ing cloddy, ill-conditioned soils, leaving them in loose, crumbly 

 condition after the ice has melted and the surplus water drained 

 off; so as to materially facilitate tillage and root penetration. 

 When, however, soils thus circumstanced are tilled or trodden 

 while too wet, they quickly become puddled, being practically 

 reduced to single-grain structure. (See this chapt. p. no). 

 Hence the injury caused by allowing cattle to range in winter 

 on cultivated land subject to freezing and thawing, which it 

 sometimes takes years to correct. 



A disagreeable effect often produced by the freezing and 

 thawing of wet lands is the " heaving-cut " of grain, result- 

 ing from the upward expansion of the surface soil in freezing, 

 that may readily rupture the roots ; while on thawing, the soil 

 surrounding the upheaved stool is apt to settle down, especially 

 in case of a rain, leaving the stool and roots exposed either to 

 drying or freezing, as the case may be. Hence the desire of 

 grain farmers in northern climates, for a sufficient covering of 

 snow to protect the fall-sown grain, rather than an '' open 

 winter," during which the grain is exposed to alternate freezes 

 and thaws, or extreme cold. 



In certain soils, notably in those liable to crusting (p. 117), 

 instead of heaving the soil, the water in freezing emerges bodily 

 from small cracks, in foliated or wire-like forms ("ice- 

 flowers") resembling those of native silver, and formed sub- 

 stantially in the same way, by a kind of " wire-drawing " pro- 

 cess, aided by crystallization. 



Small ice-crystals formed on the surface of small crevices filled with 

 water cause others to be formed at their lower ends, and the expansion 

 occurring in freezing, forces the ice upward ; the process repeating 

 itself under favorable conditions, until the stalks or sheets of ribbed ice 

 grow to a height of several inches. This phenomenon is especially 

 frequent in the middle cotton States -Arkansas, Tennessee, northern 

 Mississippi, etc., where frequent changes from rainstorms or thaws to 

 cold northwest winds occur in winter. 



