August, 1955 



EvERS: Hii.i. Prairiks of Iiiinois 



401 



Fig. 16. — Part of the west-facing slope of Swarnes hill prairie at Hamburg, Calhoun 

 County- Etliinacea, Melilotus, and Psoralea were common on this slope. 



of the monument divided the prairie al- 

 most equally into pastured and unpas- 

 tured areas. The pastured segment occu- 

 pied a west-facing slope, Hg. 16, the un- 

 pastured a west- and southwest-facing 

 slope. The unpastured surface that bor- 

 dered the rock ledge was stony, level near 

 the ledge, and gradually steepening up- 

 ward from the ledge. Bouteloua cttrti- 

 pendula was there locally dominant. In- 

 terspaces contained many indi\iduals of 

 Houstonia nigricans. The unpastured 

 prairie of the steeper slopes and the top 

 of the loess-capped blulf were dominated 

 by Andropogon scoparius. Scattered 

 clumps of Bouteloua curtipendula and J- 

 gerardi were present, and Asclepias steno- 

 phylla occurred occasionally in the inter- 

 spaces. The pastured slope supported a 

 prairie that was dominated by A. sco- 

 parius. Near the top of the bluff, as well 

 as at the top, Rhus glabra was locally 

 dominant. Psoralea tenuiflora was com- 

 mon in the pastured prairie area. Swarnes 

 prairie was visited September 7, 1949; 

 April 14, Mav 27, Julv 1, and August 12, 

 1950: and September' 27. 1951. 



Along Rock, Sangamon, and Illinois 

 Ri\ers 



Devil's Backbone. — The bluff-ridge 

 that extends along the Rock River in the 

 northeast quarter of section 16, T. 23 N., 

 R. 10 E., south of Oregon, Ogle County, 

 is gi\en the name Dexil's Backbone on 

 the Dixon quadrangle of the United 

 States Geological Survey topographic map. 

 St. Peter sandstone underlies this ridge. 

 When the ridge was last seen, one south- 

 east- and two northeast-facing prairie 

 openings occupied the upper stonv and 

 sandy slopes. Sandstone fragments were 

 abundant on the northeast-facing slope. 

 The openings on this slope were covered 

 with prairie in which Poa pratensis was 

 very abundant, Andropogon scoparius 

 less abundant, and Bouteloua curtipen- 

 dula scattered throughout. Synthyris bul- 

 lii also grew there. The southeast-facing 

 opening was a sand prairie on a slope. 

 A . scoparius was there the dominant grass. 

 Selaginella rupestris, together with mosses 

 and Androsace occidentalis , grew in the 

 interspaces. Devil's Backbone was visited 



