ECOLOGICAL SUCCESSION. 15 



Pettibone Creek is similar to Bull Creek, but a little smaller. 

 Its length does not exceed one and three fourths miles. 



County Line Creek is about twelve miles farther south. It 



differs from the others in being smaller. It also divides into 



two branches at a distance of only three sixteenths of a mile from 



mouth and the length with tributaries is about one half 



mile. 



Glencoe Brook is about . in; mile south of County Line Creek and 

 has a total available length, so far as fish are concerned, of only 

 ,i few rod-. 



The-e four -tream- arc cl-el\ < < >mparable. They all rise in 

 a moraine which -land- 1 -tu en i.o and loo feel .ibo\e the lake. 

 It- height at the Like, or point neare.-t the lake, i- about <>o feet 

 in everj Case, With the excepti-m of the lower courses of Bull 

 (nek and iVuibom- ( 'n ek, all are composed of strictly inter- 

 mittent riffle- ami |n i in. men- pt in umi-ual seasons) pool-. 

 \\ e will refer to the-c .1- the North Slmre -tream-. In addition 

 to the-r. t\\o other -tream- uete studie<l for comparison 

 Thorn-Hut ti i In Id (i.ek and Ilick"i\ ( 'reek, including it- west 



branch. 



Ilitkory < ilillcreiit from the other-. It drain- a 



number o| mar-lu-- and i- pel maiiciit . Its upper cmir-e i- \.r 

 than that of the north -lion- -tream-; it i- -lu^ii-h and meander- 

 through prairie mat-he- uilh only a very .-light fall. The lex el 

 of tin- part of tin- Mieam n piv-ein- that of a depre ion betueeii 

 glacial rid'.. - ' .. >ldth\\ ait . '" . So far as the pn-eiit c\ cle of 

 erosion i- coiK-erned ^ali-burx . '07 , erosion ha- iiroceed.d as 

 lai- as Marlex. lie|o\\ thi- point the -tream i- a typical .-\\ift 

 brook. 



Thorn-Butterfidd (>(<( i- intermediate betueeii lliekoiy 

 l "reek and the north -lime -tream-. The -ouiheru branch of 

 Butterfield Creek, near Matte-i'ii, 111., i- -hi^gi-h, but ha- inter- 

 mittent riffle- and permanent pool-. 

 History of the Region. 



\\'h.'ii the \\'i-con-in ie -heet retreated from il- maximum 

 extent, which lax U xoiid the center of the -late of I'linoi-. the 

 edge of one of it-, lobes Atuo.,.1 and (ioldt hwait . 'oM 1 took up 

 a po-ition a texv mile- oiit-ide of, and parallel x\ith, the prc-eiit 



