THE WEATHERED ZONE 1 79 



ous exposures of this peaty material alternating with sand beds 

 may be seen in ravines in that vicinity. 



In October 1896, Professor Chamberlin and the writer 

 examined together numerous exposures of the Sangamon soil 

 in the portion of eastern Illinois south of the limits of the Wis- 

 consin drift, chiefly in Cumberland, Coles, and Shelby counties. 

 North of Greenup there are exposures where the subsoil beneath 

 the Sangamon soil is traversed by branching rootlike tubes 

 one to two inches in diameter, which were easily traced ten to 

 twelve inches below the soil proper. These tubes are filled with 

 the black soil which apparently settled into them upon the decay 

 of tree roots. There seems to us little question that the San- 

 gamon soil here supported a forest. The till below this soil 

 in these counties shows leaching to a depth of several feet. 

 It also presents weathered cracks and seams extending down a 

 depth of 20 feet or more. Similar leaching and weathering 

 below the Sangamon soil has been observed by the writer in 

 several other counties in southeastern Illinois, and in Vigo, 

 Clay, and Sullivan counties in southwestern Indiana, thus 

 extending it to the southeast border of the Illinois lobe. 



Returning to western Illinois, excellent exposures of black 

 soil and leached subsoil are found along the Santa Fe railway 

 in eastern Knox county. The soil may be seen distinctly at a 

 distance of nearly one-fourth mile. It is of a deep black color,, 

 resembling the surface muck found in flat portions of the uplands. 

 The till beneath it has been leached to a depth of about four feet. 

 The loess has a thickness of 12 feet, and is slightly calcareous 

 in the lower portion. The entire leaching of the till may confi- 

 dently be referred to a date earlier than the loess deposition. 



At Galva, 111., a black soil at the base of the loess is well 

 exposed in a clay pit at the brick yards east of the city. A 

 large log was found imbedded in this soil, which here has a 

 depth of two feet. The overlying loess is 15 feet in depth. 

 A well at the brick yards penetrated 40 feet of till below the 

 buried soil, of which the upper 30 feet has a yellow color and 

 the remainder a blue-gray color. 



