CHICAGO AND VICINITT. 



15 



shrub is the witch hazel {Hamamdis Virginiand). The herbaceous 

 plants are notoriously vernal forms, such as Hepatica, Thalictrum, 

 Trillium, Mitella, Dicentra, Sanguinaria (Bloodroot); mosses abound 

 and liverworts are frequent. A ravine with the above vegetation is 

 shown in fig. 2. We can explain this flora only by regarding it as 



v^ 



Fig. 2 —Ravine at Glencoe wi h a mesophytic forest vegetation on the slopes (temporary 

 climax). Presence of erosive forces indicated by leaning trees. Water commonly present in 

 the stream bed. 



having reached a temporary climax. Ravine conditions are more 

 favorable for plants than those that precede or follow. .The instability 

 and exposure of the gully have gone; in their place there is protection 

 from wind and exposure. The shade and topography favor the collec- 

 tion and conservation of moisture, and as a result there is a rapid 

 development into a high-grade forest, as outlined above. 



Rock ravines are much less common in the Chicago area than are 

 those of clay, since the underlying limestone rarely comes near the 

 surface. Excellent illustrations of stream gorges are to be seen at 

 Lockport, and also in various tributaries of the Illinois river near 

 Starved Rock. A striking difference between these rock gorges or 



