36 BIG SPRING PRAIRIE. 
From the above data, we see that the surface soil 
has lost 37% per cent. in volume, the soil ata depth 
of 10 to 12 in. 50 per cent., while the soil from a depth 
of 6 feet lost 56% per cent. 
Under natural conditions, the soil will not dry as 
thoroughly, and in consequence will not lose as great a 
per cent. in drying, perhaps considerably less than half; 
but the ratio of loss will remain approximately the 
same. ‘he soil from near the surface lost less in vol- 
ume because it contained a smaller amount of water, and 
because the vegetable matter of which it is chiefly com- 
posed had already undergone some oxidation. 
Chemistry teaches us that a slow oxidation will 
practically accomplish in the course of years what a rap- 
id combustion will accomplish in a few hours. 
The burning of the deeper soil gave a loss of 78% 
per cent., of the soil from near the surface 70? per cent. 
making a difference of 8 percent. Thusa partial oxi- 
dation of soil had taken place in the latter and a conse- 
quent decrease in volume resulted. As this area had 
been drained but a few years, we can gain some idea of 
the importance of this phase of the subject. A com- 
plete oxidation of the vegetable portion of the soil will 
cause approximately the same decrease in general level 
as the burning of the soil, which has been occurring of 
late. 
There are four causes at work in reducing the gen- 
eral level of this area: 
Ist. Withdrawal of the water from the soil and the 
consequent shrinkage in volume as determined by direct 
experiment. 
2d. Drainage produces aeration of soil; and the 
resulting oxidation of its vegetable remains, by which 
great portions pass off as gases, cause the remains to 
settle more closely together. — 
3d. Burning of the soil, which produces most 
rapid and greatest difference in level. 
