152 ILLINOIS STATE ACADEMY OF SCIENCE 



THE PLANT ECOLOGY OF THE ROCK RIVER WOOD- 

 LANDS OF OGLE COUNTY, ILLINOIS 



H. DE Forest, University of Chicago, 1920 



INTRODUCTION 



Ogle County is located in the northern part of Illinois 

 in the second tier of counties just west of the center line of 

 the state. It is an irregular parallelogram in outline, some 

 39 miles in its widest west-east and 29 in its north-south 

 direction. The total area is about 750 square miles. The 

 area dealt with specifically in this paper comprises some 

 75 to 80 square miles along the Rock River, with a small 

 area to the west of the Rock on Pine Creek. 



The larger part of the surface of the county is overlaid 

 by glacial drift, generally so thinly as rarely to attain 

 even 20 feet depth, and reaching its maximum of about 

 125 feet only in the northwestern part. The elevations 

 above sea level run from about 700 to 900 feet. The Rock 

 River, a moderate sized stream, takes a general north-east 

 to south-west course through the middle of the county, with 

 three or four main tributary streams entering it from the 

 west and the east. It makes a great bend near the southern 

 border of the county. The course of the Rock takes it 

 through lowan drift, which overlays more than half the 

 county and affords good drainage without swamps. From 

 the southern boundary an irregular area, varying from a 

 few hundred feet to 10 or 12 miles wide, underlain by St. 

 Peter's sandstone, extends northward along the Rock on 

 either side for about two-thirds of the distance to the north- 

 ern boundary. The remainder of the county, with the ex- 

 ception of a small area of the sand-stone at the west bound- 

 ary and some shales at the south-east comer, is under- 

 lain by Trenton-Galena limestones. Outcrops of both sand- 

 stone and limestone in cliffs and walls occur along streams. 



The larger part of the county is undulating prairie. Here 

 occur groves of upland prairie oaks. Along the river and 

 creeks the country is more or less hilly. Here there is a 

 fair growth of woodlands. 



