8 A NATURALIST IN THE GREAT LAKES REGION 



precipitous hills (Fig. 8). The rock of the region is a rather soft 

 sandstone and the river has cut its way deeply into this, scouring 

 out its valley as it shifts from side to side in its meandering way. 

 The surrounding country is slightly rolling farm land, giving 

 the impression of a level plain. It is startling to walk or drive 

 across this country and then suddenly find yourself on the brink 

 of a deep valley with precipitous sides, loo feet sheer, and look 



Fig. 8. — The Valley of the IHinois River, looking from Starved Rock to the 

 bluffs on the opposite side. 



across to the opposite side, 3 or 4 miles away. The tributary 

 streams flowing to the river from the plain plunge down in foam- 

 ing falls wliich eat their way back through the sandstone, form- 

 ing narrow chasms that end abruptly at their head in a rock wall 

 down which, when the stream is full, the water thunders (Fig. 9). 

 There is a small but very interesting rock canyon cut in the 

 limestone on the south side of the valley of the '^ Calumet 

 Feeder" i mile east of ''Sag" Station on the Chicago & Joliet 

 Interurban (Fig. 393). Fraction Run cuts through the limestone 



