138 THE ILLINOIS GLACIAL LOBE. 



leached by atmospheric action, a feature which seems to indicate that the 

 deposition of the loess closely followed the withdrawal of the ice^ 



Within the limits of the Pecatonica lobe there is a very sandy till 

 liberally set with small fragments of limestone and usually leached to a 

 depth of 2 to 4 feet. East from Rock River, in Winnebago and Boone 

 counties, the till is, on the whole, less sandy than west of that stream. 

 Several exposures were noted in railway cuttings between Roscoe and 

 Caledonia in which the till becomes calcareous at a depth of but 1J to 2 

 feet, but there is usually leaching to a depth of 3 feet or more. 



Exposures of Iowan till were noted by the writer on the south and 

 east borders of the city of Dixon. One on Second street and Dumont ave- 

 nue shows a thin sandy capping, beneath which is fresh-looking calcareous 

 till. Farther east the sand disappears, yet the till is found to have suffered 

 leaching only to a depth of 3 or 4 feet and is markedly fresher than the 

 Illinoian. In the south part of Dixon, along - the Chicago and Northwestern 

 Railway, the first cutting east of the crossing- of the Illinois Central Rail- 

 road shows a calcareous sand, apparently Iowan, resting on a leached till 

 in which no effervescence with acid could be obtained within 5 or 6 feet of 

 top. In exposures farther east a thin capping of loess rests directly on the 

 Illinoian till. There appears, therefore, to be only a patchy deposit of 

 Iowan drift in the vicinity of this city. Hershey has noted several expo- 

 sures of the Iowan between Dixon and Sterling, and west from there to 

 Rock Island Junction. The common phase is a very sandy till, in places 

 becoming clear sand. 



In railway cuttings east from Polo low knolls belonging to the Iowan 

 drift have been well exposed. They are capped by about 4 feet of loess- 

 like silt, beneath which the till is found to be calcareous from top to bottom. 

 It is more clayey than in exposures near Dixon and Sterling. In this 

 locality the Iowan drift appears to be restricted mainly to the knolls, for 

 exposures of the Illinoian drift appear in ditches made by the railway in 

 crossing the low tracts aim mg the knolls. At the village of Stratford, 5 

 miles east of Polo, the railway exposes a bed of fossil iferous silt at the 

 base of the Iowan drift, resting on an old land surface formed on the 

 Illinoian. The fossils appear to be entirety of one species (Succinea avara). 

 In two other localities fossiliferous silts have been found at the base of the 

 Iowan, one being in the railway cuttings on the Illinois Central immediately 

 west of Irene, in southwestern Boone County, and another in the railway 



