42 BIG SPRING PRAIRIE. 
area to the mesophytic condition. The above represents 
the curve if only one effort at drainage has been made. 
If the ditches are cleaned out or deepened, new curves 
must be accordingly introduced at the proper stage. 
If the soil takes fire after drainage, and a severe 
burn ensues, the curve will need adjustment as follows: 
XEROPHYTIC 
MESOPHYTIC 
HYDROPHYTIC * 
FIGURE 8. RETROGRESSION AS RESULT OF THE BURNING OF SOIL. 
a to b—Advance under natural conditions. 
6 to c—Advance under artificial drainage. 
c to d—Stage of settling before prairie fire. 
d to e—Retrogression as result of prairie fire. 
ée to f—Advance under natural conditions. 
As before stated, the first ditches were dug about 
1860, but by 1890 certain portions of prairie had so far 
reverted toward former conditions that a joint county 
ditch was petitioned for and granted by the proper au- 
thorities of Seneca and Hancock counties. This ditch 
was constructed in 1891 and is known as the Bower 
Ditch as represented on Map I. 
Figure 9 gives an illustration of it some distance be- 
pond the prairie area. The greater portion of this out- 
let is cut through a considerable thickness of clay now 
quite firm. ‘The muck above it has undergone consid- 
erable oxidation and consequent settling. ‘This outlet 
will furnish adequate drainage for great portions of this. 
prairie for many years to come. 
In 1897 it was found necessary to deepen the outlet 
of the Brown Ditch at southern end of prairie. In order 
