52 OSCAR H. HERSHEY 



resembling fine yellow sand. By a continuance of the process 

 the crystals are dissolved, leaving a slight residue which, accumu- 

 lating to a thickness of two to ten feet, becomes a highly 

 oxidized, dark red, very fine-grained, structureless clay. Certain 

 layers of the dolomite abound in chert, which breaks up into 

 angular fragments, averaging about the size of a walnut. These 

 abound in the residuary clay, and on hillsides often pass hori- 

 zontally from the solid rock into the red clay, with but little 

 disturbance of the lines of stratification. This is one of the 

 strongest proofs of the undisturbed nature of the residuary clay 

 at the localities previously mentioned. In fissures and pit- 

 shaped holes in the surface of the rock, the red clay may extend 

 down from ten to thirty feet. This particular form of its occur- 

 rence can be observed in almost any rock-cutting in the county.' 

 I . The first effect of the contact between the base of the glacier 

 and the mantle of residuary clay, was a rearrangment of the 

 latter. It was pushed forward and downward, but as its down- 

 ward progress was limited to a slight compression, the effect 

 was a crushing or kneading of the mass. The faint evidence of 

 stratification in the undisturbed deposit furnished by the layers 

 of chert, was totally destroyed and the fragmental chert 

 scattered indiscriminately through the mass. All deposits of 

 rearranged residuary clay are referred to this stage when they 

 contain no foreign material whatever. As they, in many cases 

 can be. proven to have been moved but a very short distance, 

 their transportation and deposition were clearly exclusively sub- 

 glacial.^ . 



^ For a thorough discussion of the residuary material accumulating over the 

 Galena limestone in unglaciated areas, the reader is referred to Chamberlin and 

 Salisbury's excellent report on the superficial geology of the Wisconsin Driftless Area 

 in the Sixth Annual Report of the U. S. Geological Survey. 



"A careful study of the county of Stephenson would probably afford several hun- 

 dred localities — of very limited extent, however — where th^ process of till making 

 was stopped in this first stage. Good exposures can be found by following the C. G. 

 W. R. R. from South Freeport to Egan, or the I. C. R. R. from Feeeport to Everts. 

 Another, exposed in a small ravine on the south side of Yellow creek, is important 

 from the fact that the rearranged residuary cherty clay has been pushed off of its 

 original rock ridge onto the surface of a lake deposit. 



