120 THE ILLINOIS GLACIAL LOBE. 



or 3 feet from the surface. The Kansan till, as noted above, is commonly 

 characterized by vertical fissures and shows a tendency to fracture in rec- 

 tangular blocks. Along the lines of the fissures the brown stain often 

 extends some distance into the blue or unoxidized portion of the sheet, thus 

 extending the limits of oxidation still lower than the general zone of oxida- 

 tion. As previously stated, the amount of leaching and oxidation at the 

 Yarmouth stage appears to be about as great as in all post-Illinoian time. 



There are, as above noted, places where the Illinoian till rests directly 

 upon an unleached Kansan, but in such places the oxidation and vertical 

 Assuring are present to testify to the changes effected in the Kansan sheet. 

 The absence of a leached zone at the top of the Kansan in such places is 

 readily accounted for through removal by the Illinoian ice sheet. It is 

 perhaps more remarkable that the leached zone is so well preserved than 

 that it should have been occasionally removed by the Illinoian ice invasion. 



BTJBIED SOIL, PEAT, ETC. 



The accumulation of beds of peat at the surface of the Kansan drift, 

 prior to the Illinoian ice invasion, constitutes as impressive an evidence of a 

 prolonged interval as the leached and reddened surface. In the Yarmouth 

 section the peat has a depth of 15 feet while underlying beds of sandy 

 clay, and sand carrying bits of wood, probably also to be classified as inter- 

 glacial, extend the depth of the Yarmouth deposits to 43 feet. Buried soil 

 of black color and beds of peat have attracted the attention of well diggers 

 in nearly every township of the region of overlap in southeastern Iowa, 

 and specimens of the peat obtained from wells are preserved at many of the 

 farm houses. Along the border of the Illinoian the soil is usually found at 

 about the general level of the upland portion of the Kansan drift surface 

 and may be referred with confidence to the Yarmouth stage, but occa- 

 sionally it occurs below that level. In such instances, so far as the writer 

 is aware> no soil has been noted at a level corresponding- to the upland sur- 

 face of the Kansan. The presumption is that the soil occurs in interglacial 

 valleys which had been cut into the Kansan prior to the Illinoian invasion, 

 and that the entire till deposit above the soil is Illinoian. The erosion thus 

 indicated commonly shows a depth of less than 50 feet and harmonizes with 

 the depth of pre-Illinoian valley erosion of the drift outside the limits of the 

 Illinoian drift. There is, however, an occasional example of the occurrence 



