BIG SPRING PRAIRIE. 



41 



Horizontal lines indicate time. Vertical lines in- 

 dicate rapidity of filling up or change. 



a — First bulrush or tattail making its appearance. 

 b to c — Curve of advance from shallow lake to 



marsh. 

 c to d — Curve of advance from marsh to semi-marsh. 

 d to e — Curve of advance from semi-marsh to meso- 



phytic prairie. 



Under artificial drainage this curve must be modi- 

 fied to meet the new conditions, and hence the follow- 

 ing diagram will illustrate it: 



"KEROPHYTIC 



MESOPHYTIC 



HYDROPHYTIC ^ 



STGTJEE 7. 



DIAGRAM OF ADTANCE AND EETEOGEESSION UNDEE AETIFI- 

 CIAL DEAINAGE. 



a — Appearance of first bulrush or cattail. 

 a to b — Advance under natural drainage. 

 b to c — Effect of artificial drainage. 

 c to d — Settling of soil and erosion. 



But the condition of greatest water content of soil 

 will not be reached until the outlet ditch becomes com- 

 pletely clogged up with plant remains whose accumu- 

 lation will be greater here than where there is less 

 moisture. Consequently a barrier retarding drainage 

 will be built up and the conditions on the originally 

 ■drained portion will for a time become more hydro- 

 phytic as indicated by the curve 'W to ^." When "£■" 

 greatest degree of marshiness has been attained, the 

 natural process of advance will again tend to carry the 



