ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 487 



INTRODUCTION 



Available evidence points to the end of the Woodfordian Substage of the 

 Wisconsinan Stage of the Pleistocene at about 12,500 radiocarbon years B.P. 

 (Willman and Frye, 1970) . Dissipation of the last Woodfordian glaciers in the 

 Lake Michigan Basin left, here and there, isolated masses of glacial ice, which, 

 protected by mantling debris, slowly melted; in closed or poorly drained basins 

 in a morainal topography, these glacial ice blocks formed ponds and lakes of 

 various sizes and shapes. As the climate ameliorated, aquatic plants and ani- 

 mals colonized these small lakes, many of which terminated as peat-covered bogs , 



Two such bogs (figs. 1 and 2) are the subject of this study; one of them 

 is situated on the Delmar Ford farm, 1.5 miles north and 4 miles east of the vil- 

 lage of Strawn, in the SWi SWi SEi section 32,T.26N.,R. 8E., Livingston 

 County, Illinois (Strawn NE Section, localities 135-1, 135-2). The second bog 

 is situated about 85 miles north of the first, and about 2 3/4 miles west-south- 

 west of Batavia, on property of Batavia Soil Builders, Paul Wasser, president. 

 The hand-auger boring that provided the data for the Batavia West Section 

 (locality 136) is on this property in the SEi SEi section 24, T. 3 9 N. , R. 7 E. , 

 Kane County, Illinois. At each of the localities, property owners were graciously 

 cooperative; their assistance is gratefully acknowledged. 



Volo Bog, situated northwest of the city of Chicago, in Lake County, 

 Illinois, has been intensively studied (McComas, Kempton, and Hinkley, 1972) 

 geologically and hydrologically. In addition to describing the portion of the bog 

 with a pH in the acid range, the authors (who incorrectly refer to Volo Bog as 

 unique in Illinois because "no other bogs in Illinois have open-water ponds") 

 describe a portion in which Typha and sedges produce an alkaline sediment, but 

 they make no reference to fossil shells in these basic deposits. Their study of 

 the time framework of the development of the Volo Bog corresponds well with the 

 available dates for the Strawn NE and Batavia W bogs; especially interesting 

 perhaps is the date they obtained from the base of about 5 feet of peat, 2, 100 ± 

 200 years B.P. (ISGS-49) , which is almost identical with the date obtained from 

 a similar peat deposit at Batavia W (1,870 ± 200 B.P. , ISGS-134) . 



Baker (1910) investigated the Skokie Bog with special reference to the 

 molluscan faunas living there at the time; he did not explore the sediments in 

 the bog for fossil mollusks. 



STRAWN NORTHEAST LOCALITY 



The two hand-auger holes bored at the Strawn Northeast locality (135-1, 

 135-2, fig. 1) were made at the water's edge of a small lake maintained by a 

 brook that enters the bog from the Paxton Moraine to the east; a colony of 

 beavers regulates the water level of the lake by a dam which these animals keep 

 in good repair. The depression in which the fossiliferous sediments have accu- 

 mulated (fig. 1) seems to have been occupied by a glacial ice remnant in a 

 morainal topography. The present lake is about 200 by 400 yards, but deposits 

 indicate that the lake was originally at least twice this size. Only a 12 to 18 

 inch layer of peat covered the bog; this was removed by operations begun in 



