154 
IOWA ACADEMY OF SCIENCE Vor.. XXVII, 1920 
run-off was rapid unless hindered. The subsurface of the timbered 
slope shows almost as great a gain as the surface, while in the 
open the corresponding gain is only a slight one. This would in- 
dicate again the greater power of obstructing run-off in the tim- 
bered slope, with the resultant benefit to the lower soil layers. 
At the foot of the slopes the surface in both open and timber 
shows a distinct increase, but the subsurface and subsoils drop. 
This drop is the more rapid on the open slope. An important ob- 
servation to be made at this point is that there is a marked in- 
crease lagging over into the dry period of August 6 to 11. This 
is decidedly more marked for the timber than for the open. The 
surface soils during this period show practically no increase in 
the timber and a decrease in the open. Then too, the subsoil of 
the open begins to show a drop following August 8, while in the 
timber there is a rise until August 11. Thus, there is further evi- 
dence of the gravitational movement toward the lower soil layers 
as well as toward the foot of the slopes, and also further evidence 
of the delaying or prolonging of the response to rainfall over a 
longer period in the timber soil, especially on the lower part of 
the slope. 
The rain of August 13 was of a character which would pro- 
duce moderate run-off. As a result, the response is manifested 
in general in all the timber soils except those at the foot of the 
slope. At the foot the effect of the rainfall is apparently de- 
layed until after the 14th. In the open, however, there is evident 
very little or no rise in subsoils or in the subsurface soils at the 
middle and foot of the slope. Here, as before, the timber soils 
show clearly the greater amount of precipitation absorbed. 
Moreover, consideration of the curves for the period subse- 
quent to August 14, bears out other observations previously made. 
No precipitation is recorded until the 17th, but there is an increase 
in moisture content as follows : 
For the Open Slope ; Top of slope ; in subsurface and subsoil. Middle 
of slope; in subsurface and subsoil. Foot of slope; in subsoil. 
For the Timbered Slope: Top of slope; no increase. Middle of 
slope; in subsoil. Foot of slope; in surface, subsurface and subsoil. 
With the exception of the foot of the timbered slope these in- 
creases for this period are accompanied by decreases in the res- 
pective surface soils. Furthermore, the increase in the timber 
soils is much greater than that in the open soils, this being partic- 
ularly true for the lower parts of the slopes, and the increase at 
the foot of the timber slope extends into the subsurface and sur- 
