OUTER MORAINE OF THE MIAMI LOBE. 



313 



but they occur also on the uplands. A good illustration of such knolls in 

 the latter situation niay be found on the elevated tract north of Brookville, 

 Ind., at an altitude 400 feet above the Whitewater Valley. Here two 

 gravel knolls were observed, each about 20 feet in height, standing in the 

 midst of the till swells of the moraine and in no way connected with drain- 

 age lines. Having considered the question whether those which occur in 

 the valleys may not have been sculptured into their present forms by post- 

 glacial drainage erosion, the writer is convinced that their origin is inde- 

 pendent of the present streams. They were neither deposited by them nor 

 are they remnants left by erosion. They usually present the hummocky 

 irregular surface characteristic of morainic deposits. Only the knolls, how- 

 ever, are composed largely of assorted material, the low-lying tracts among 

 them, as shown by well borings, being frequently underlain by till. 



We may now pass to a more detailed description of the noteworthy 

 illustrations of drift structure and thickness. The discussion begins with 

 the tract in the Scioto-Miami reentrant angle. 



At West Liberty, Ohio, in the valley of Mad River, a gas well j^ene- 

 trated 216 feet of drift, largely sand and gravel, while in the same valley 

 1^ miles east there are exposures of limestone along Mackocheek Creek at 

 about the altitude of West Liberty, and ledges still farther east rise to a 

 height of 100 feet above the village, or 1,200 feet above tide. Wells ai'e 

 often obtained at 25 to 50 feet on the morainic ridges, after penetrating a 

 stony till. 



Several deep wells have been made in the vicinity of Urbana, of which 

 the following tabulated records were furnished by T. F. Moses, formerly of 

 that city: 



Table of wells near Urbana. 



Tannery well 



Power well 



Glue factory well 

 Sycamore well . . 

 Citizens, No. 1 . . 



Feet. 

 1,044 



1,001 



1,020 



1,000 



1,061 



150 

 133 

 102 

 150 

 150 



