DISCUSSION OF ECOLOGICAL FACTOUS 47 



The influence of the more important ecological factors upon 

 the prairie formation is briefly discussed in the following 

 pages. The prairie upon which the formational work was 

 conducted lies about three miles west by south of Nebraska 

 City, along the Burlington railroad. It measures 800 meters 

 on a side and has an elevation of 305 meters above sea-level. 

 The highest point is located south of the center on the most 

 important ridge called, for convenience, Great ridge. This 

 elevation, which is an extension of higher land lying to th6 

 south, passes north and northeast through the formation, 

 dividing it into two unequal portions, and terminates 

 abruptly in the northeast corner of the prairie. In its course 

 it gradually decreases in altitude and gives off to the north- 

 west and east secondary ridges of note. The lowest point, 

 exclusive of the creek-bed, is northwest from the center in 

 the meadow formation. The difference of elevation between 

 the highest and lowest points is, by actual measurements, 24 

 meters. 



On the south of this prairie lies the regular section road, 

 beyond which are cultivated fields ; to the east and west also 

 are culture formations, and a pasture and railroad 

 bounds the north. A hedge of Toxylon pomiferum (osage 

 orange) forms a dividing line on the east between prairie and 

 field for 400 meters, and for the same distance on the north 

 between prairie and pasture. This hedge serves as a basis 

 for woodland species to gain access to the prairie. 



The surface as a whole gradually inclines to the north 

 and is rolling, a character due entirely to the erosive action 

 of water. The slopes of the south are more gradual than 

 those of the north; likewise those of the east are less abrupt 

 than those of the west. South Table creek flows through 

 the northern half of the prairie, cutting off perhajjs ten or 

 twelve hectares from the main body. It enters midway on 

 the west, meanders east by northeastj and leaves at the north- 

 east corner. The banks of this creek in many places are 

 steep, ranging from six to twelve meters high, and generally 



