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IOWA ACADEMY OF SCIENCE Voi.. XXVII, 1920 
able of maintaining the higher moisture content in all instances 
but in the subsoil, and here there is found almost a clay soil in 
the open. 
The average content of the timber soils as well as both maxi- 
mum and minimum contents are above those for the open soils, 
with an exception made of the heavier subsoils of the open slope. 
This is most clearly emphasized toward the latter part of the 
season. The fact that, in the open, in spite of the greater reten- 
tive power of the heavier subsoils, the minimum drops to a point 
almost equal to or lower than that for the timber soils, is im- 
portant, since, as has been shown by Fuller and by Briggs and 
Shantz and others, the wilting coefficients of such soils are higher 
than for the sandier soils. Furthermore the wilting coefficient of 
these soils would be expected to be above that of the timber soils, 
because as Brown and others have shown the wilting coefficient 
rises with increased evaporation of the air. 
Throughout all of the above the greater absorptive power of the 
timber soils is apparent, as well as the influence this has upon the 
moisture content of the various soil layers. This is perhaps mpst 
strikingly manifested at the middle of the slopes where precipita- 
tion with rapid run-off has the least opportunity to penetrate into 
the subsurface and subsoils. It is found that on the open slope 
the subsurface soils at the middle and foot show the lowest con- 
stant averages of any of the soils, while the same relation does 
not exist in the timber. 
The run-off is, therefore, without question the greatest on the 
open slopes. The result of this is especially marked in the sub- 
surface and subsoil regions where we frequently find little or 
no response to rainfall in the open but a decided upward tendency 
of the curves for the timber areas. This difference seems more 
marked as the season progresses. 
There is apparent a distinct gravitational movement of soil 
water from upper to lower soil layers and from the top toward 
the foot of the slopes. The lower soil areas rather uniformly 
show a continued increase in moisture content after the surface 
layers have begun to exhibit a drop. The difference in the rate 
at which gravitational movement takes place is not finally estab- 
lished, but every indication points to its being most rapid on the 
open slope following precipitation, and to its being in greater 
quantity, steadier, and distributed throughout a longer period in 
the timber soils. Furthermore, in these latter soils there is evi- 
dence of the increased volume of gravitational moisture and the 
