NATURE AND FORMATION OF SOILS. 5 



within the soil is increased, producing a certain 

 amount of heat. This heat, when transmitted 

 to the air, causes it to expand and thus become 

 Hghter, when the cooler and heavier air rushes 

 in from the sides, forces it upward, and wind re- 

 sults ; if transmitted to the water, the increase 

 of the molecular motion of the water overcomes 

 the force of cohesion, and evaporation ensues. 



As the vapor rises it gradually becomes cooled 

 and condensed, and clouds composed of minute 

 particles of water ^ are formed; these minute 

 particles of water, after further cooling and 

 condensing, are united by cohesion into drops, 

 and are drawn back to the earth by the force 

 of gravity, in the form of rain, snow, or hail. 

 These few examples may serve to show how the 

 sun's energy is transformed into a multitude of 

 activities. 



^.—FACTORS OF SOIL FORMATION. 

 I. The Atmosphere. 



I. It Regulates the T'empcr attire. — On winter 

 nights the lower layer of air — especiall)- if laden 

 with dust and moisture — acts as a blanket in 

 checking radiation of heat from the earth's 

 surface. But, in the intense heat of summer, 

 this lower layer of air would, through radiation 



* "Clouds formed at temperature above 32^ consist of minute 

 spherical drops of water 1-4000 to i-iooo of an inch in diameter; 

 those formed below 32"^ consist of minute ice spicules which in- 

 crease in size and become snow." — 'Da.y'x^'' Meteorology,-^^. 159, 160. 



