ESKERS OF NORTHWESTERN ILLINOIS. 81 



a lake in the portion of the Pecatonica Basin west from the ice margin, for 

 this basin is open only to the east, and in all probability a lake would 

 occupy it outside the edge of the ice sheet and become expanded eastward 

 with the retreat of the ice. 



So far as examined, nothing was found either by Hershev or by the 

 writer to indicate that the structure of this belt of ridges differs from that 

 commonly displayed by eskers. In several of the ridges the upper portion 

 is found to consist of a coarse gravel and cobble, but there are other ridges 

 composed largely of sand and fine gravel. The pebbles are chiefly lime- 

 stone, and are largely of local derivation. Hershev maintains that they 

 are derived by direct wear from the neighboring ledges rather than as a 

 residue from the till, but the writer is inclined to question this interpretation, 

 since the structure of the till and of the eskers is, so far as he has examined 

 in this district as well as elsewhere, quite similar in the kind of coarse rock 

 ingredients. 



cedarvme belt. — Hershey has traced two other lines of gravelly drift for 

 several miles in an east-west course in the portion of Stephenson County 

 north of the belt just discussed. To these he has given the names Cedar- 

 ville and Orangeville. The former belt he considers to have its beginning 

 in the valley of Rock Run, about 1J miles east of Rock City, but it can 

 not be definitely traced until it reaches the valley of Cedar Creek, about 2. 

 miles above Cedarville. It is prominently developed southeast of Cedar- 

 ville, where it rises into sharp knolls 80 or 90 feet in height, which have so- 

 obstructed the old valley of Cedar Creek as to compel the stream to cut a 

 gorge on the north side of the village. The belt is again prominent near 

 the junction of Cedar and Richland creeks, 2 miles west of Cedarville. It 

 is again prominent at the village of Damascus. The belt extends about .3 

 miles farther in a northwestward course, as a line of sharp knolls, the ter- 

 minus being about 3 miles northeast of the village of Lena. The well- 

 defined portion of this belt is about 12 miles in length, but if we consider 

 its beginning to be at Rock Run, its length is nearly 20 miles. 



orangeviiie belt. — The Orangeville belt has been only partially mapped by 

 Hershey, and is found to be best developed south of the village of Orange- 

 ville, and again just north of Winslow. At the latter point it rises into a 

 very prominent knoll with a number of associated ridges. 



HON XXXVIII 6 



