CHICAGO AND VICINlTr. 



43 



stages from Calumet lake. Skokie marsh and Hog marsh are undergo- 

 ing transformations of this character also. Sometimes with the prairie 

 grasses are a number of coarse xerophytic herbs, largely composites, as 

 Silphium laciniatum (Compass plant), i'. terebinthinaceum (Prairie dock), 



5. integrifolium (Rosin weed), Lepachys, Solidago rigida, Aster, Liatris 

 (Blazing star), with some legumes, as Amorpha ca/iesce/is (Lead plant). 



Fig. 25.— Prairie at Pullman in vvliicli tiie compass plant tSilphium) grows with the grasses. 

 This prairie is much older and drier than that shown \n/ig. 34. 



Petalostemon (Prairie clover), Melilotus (Sweet clover), and Baptisia, 

 Eryngium, Dodecatheon (Shooting star), Phlox, Allium cernuuvi (Wild 

 onion). A Silphium (Compass plant) prairie is shown iri fig. 2j. The 

 prairies of our area are in the basin of the glacial Lake Chicago, and 

 hence all may be referred to a lake or swamp origin, exactly as prairies 

 are developing from Calumet lake today. This explanation of the prairie, 

 an undoubted explanation for the cases in hand, must not be applied to 

 the great climatic prairies farther west. Whether the Chicago prairies 

 will ever become forested is a question not easily answered. There 

 are signs of it in some places, as at Stony Island, but this topic needs 

 more detailed treatment than can be given here. 



The processes outlined in -this section are rapid. The mesophytic 

 prairie or forest develops from the lake or marsh, while the region as a 

 whole still retains a young topography. Thus this mesophytic assem- 



