140 THE ILLINOIS GLACIAL LOBE. 



The reference of the soft blue clay of this section to the Iowan is 

 apparently supported by an exposure a short distance west of Round Grove, 

 where the excavations at the side of the railway show a soft till which,^ 

 though yellow at top, assumes a blue color within 3 or 4 feet of the surface. 

 It has an appearance as fresh as any exposure of Iowan till noted in 

 districts to the east. The exposure is not sufficiently deep, however, to 

 show the depth of this till or to enable one to determine whether an older 

 sheet underlies it. Directly east of Round Grove about l£ miles, the loess 

 is found to rest upon a till having leached and reddened surface, evidently 

 as old as the Illinoian. These features indicate either that the Iowan ice 

 failed to cover the district immediately east of Round Grove or that it did 

 not form a continuous sheet of till. The first interpretation seemed to the 

 writer at one time the more probable, but further reflection and considera- 

 tion of the fact that this drift sheet is somewhat patchy in the districts to 

 the northeast has led to a more favorable view of the second interpretation. 

 If the fresh-looking drift found west of Round Grove is of Iowan age, the 

 district to the east of that village was probably covered by that ice lobe. 



West and south of Morrison, on the borders of Rock Creek and east- 

 ward from its valley, sandy till of fresher appearance than the Illinoian was 

 noted at several points. In some cases it is found to be calcareous within 

 3 feet of the surface. At the point where the wagon road ascends from 

 Rock Rive:- Valley toward Spring Hill an exposure was found in which the 

 loess rests directly upon an unleached surface. It seems scarcely probable 

 that there had been erosion of the till prior to the loess deposition, for the 

 till surface there rises to its usual elevation in that locality. In the cases 

 above noted also no evidence was found of any removal of the surface por- 

 tion of the till. Exposures of till are rare in this region, partly because of 

 the shallow depth of valleys and partly because of concealment by loess. 

 The few above noted comprise all that were observed by the writer in 

 central and southern Whiteside County. 



STRI/E. 



A few exposures of striae have been found in Winnebago and Ogle 

 counties which fall within the limits of the Iowan drift sheet, but which are 

 not referred positively to that ice invasion, since they may be referable to 



