7 — 



surface of the soil-layer is protected against any invasion of warmth from 

 the air; and underneath, the temperature of the whole frozen layer is also 

 below zero, the cold from thence travelling upwards. Therefore the upper 

 surface can only thaw when the snow attains a temperature above 0", 

 that is, turns into water. Now even if a part of this water penetrates into the 

 minute cracks in the depths of the soil, it will be turned into a solid 

 state and arrest the trickling water from above. At the same time, the 

 water on the surface of the soil gets warm, a part evaporates in the air, 

 and a part warms the lower layer of soil and water, raises the temperature 

 and saturates the thawing belts of land. 



The whole question, therefore, comes to this: how quickly does the 

 soil thaw and how much snow-water succeeds in percolating. If the 

 thawing of the soil only proceeded from below upwards, then it might 

 happen that all the snow-water would be absorbed. 



But // not only proceed upwards; but downwards as well from above 

 simultaneously. 



To illustrate this I have traced the course which the process of 

 spring thawing took in 1907 in the soil of Odessa Experiment Field [fig. 1]. 

 In general this process runs just so every year, the only difference being 

 the thickness of the frozen layer and the time the thaw commences: in 

 in the south it sets in earlier; in the North — later. 



February 



20 n 



March 



Fig. 7. The proccess of thawing of the soil in spring. 

 (The frozen layer is hatched). 



Up to the 20-th February the thermometers showed that the soil 

 had frozen to 80 cm. from the surface [the frozen layer is shaded]. 

 On the 20-th of February the layer thawed to 14 cm. from the surface, 

 and the rest remained frozen. From the 1-st to the 8-th the same layer 

 of 14 cm. was again frozen up. On March the 9-th the layer thawed 

 again to 10 cm. and on the 10-th of March to 14 cm. and remained 

 in that condition until the i-st°f April. 



