4 A NATURALIST IN THE GREAT LAKES REGION 



valley, then, is largely the work of the stream it contains. The 

 whole valley, limiting hills, meanders, flood plain, cuttings, and 

 fills, may be seen in perfection in many of the smaller streams, 

 such as Salt Creek near Brookfield, Thorn Creek near Thornton, 

 Pettibone Creek at North Chicago. 



Fic. 3. — A stream cutting its banks. Photo by Fuller 



The Chicago region shows many stages in the formation of 

 the valley. Where the lake shore is high, as it is from Glencoe 

 northward or on the eastern shore from New Buffalo north, 

 the melting snows and spring rains find their way to the shore 

 along irregular depressions, then plunge down the steep bank in 

 headlong turmoil, cutting rapidly a steep-sided ravine. Gradu- 

 ally the stream eats its way back toward the relatively level 

 meadowland. You may follow down its course from where the 



