76 THE ILLINOIS GLACIAL LOBE. 



The low drift ridge of southern and western Fulton County consists of 

 till in its smoothest portions, but there are a few knolls in the northwest 

 part of Fulton County which are of gravelly constitution. In this con- 

 nection it may be remarked that the sections of wells made on knolls in 

 western Illinois so far as obtained exhibit as a rule much more till than 

 sand or gravel. In short, it may be said that the ridged drift and knolls of 

 the Illinoian sheet are generally composed mainly of till and differ but 

 little from the drift of the plane tracts which border them. But in north- 

 western Illinois the ridges of the sheet tentatively referred to the Illinoian 

 are largely of gravelly structure and some are of esker type. 



ESKERS OR GEAVELLY RIDGES OF NORTHWESTERN ILLINOIS. 



Leaf River or Adeline esker. — The largest and best-defined esker found in north- 

 western Illinois stands in the valley of Leaf River in northern Ogle County, 

 and is discussed by Hon. James Shaw in the report on Ogle County. 1 



It has been discussed more recently by Mr. Oscar Hershey, who has 

 applied to it the name Adeline, from the village of Adeline, situated near its 

 eastern end. 2 



As Judge Shaw's report was prepared before the distinguishing char- 

 acteristics of eskers were fully known, the name moraine was very naturally 

 applied to the ridge. This reference of the ridge to glacial action is of 

 interest, since Shaw had, prior to the examination of it, followed the State 

 geologist, Professor Worthen, in the support of the iceberg hypothesis as an 

 adequate explanation for the drift phenomena of northwestern Illinois. 

 Chamberlin was apparently the first to recognize this ridge as an esker, on 

 a visit made to it about 1881, in his studies preparatory to the writing of 

 the paper in the Third Annual Report, 3 The writer's examinations were 

 made in the spring of 1886. 



The esker, as may be seen by reference to PI. XII, is a practically con- 

 tinuous ridge about 12 miles in length, extending from a point 1 mile east 

 of Adeline westward to sec. 14, T. 25, R. 7 E., about 5 miles northwest 

 from Forreston. The only notable gap occurs where a branch of Leaf River 



1 Geol. of Illinois, Vol. V, 1873, pp. 108-109. 

 ! Am. Geol., Vol. XIX, 1897, pp. 200,201. 



3 Preliminary paper on the terminal moraine of the second Glacial epoch, by T. C. Chamberlin: 

 Third Ann. Eept. U. S. Geol. Survey, 1883, pp. 291-102. 



