Correspondence. 255 
small part of the time between the Kansan retreat and the lowan ad- 
vance. Unless therefore the subsequent weathering be included under 
this name, the Buchanan does not fill an interglacial stage. Were there 
no Illinioian glacial stage to break the continuity of interglacial condi- 
tions from the Kansan to the lowan stage of glaciation it would seem 
unnecessary to introduce other names. But in view of this glacial inter- 
ruption there seems need for names which will stand for the weathered 
zones above and below the Illinoian till sheet. It is for this reason 
that the name Sangamon is here proposed for a weathered zone between 
the lowan loess and the Illinoian till sheet. The name Yarmouth is 
introduced in an accompanying paper for the weathered zone between 
the Illinoian and Kansan till sheets. The name Buchanan may still be 
retained with the significance given it by Prof. Calvin; and if weathering 
be included may perhaps be used to cover the time involved in the two 
interglacial stages and intervening glacial stage which occur between 
the Kansan retreat and the lowan advance." 
The name Sangamon is taken from the county and drainage basin 
of that name in central Illinois where exposures showing the break 
between the lowan loess and Illinoian till were first discussed in print.* 
At the type locality the break is filled to a large degree with the accumu- 
lation of a bed of peaty muck. This is a feature which characterizes a 
large part of the Sangamon drainage basin and is one that is perhaps 
more likely than any other interglacial product to draw attention. It 
is not, however, the most common and widespread phase. A much 
more common phase is a reddish brown leached surface of the till sheet. 
This appears to have been developed in all places where there was good 
drainage. The black muck indicates poor drainage conditions, and 
where it is present the reddened zone is weakly developed. Leaching 
of the surface of the calcareous till is found to have reached an average 
depth of about six feet prior to the deposition of the loess. The loess 
deposition is referred chiefly to the lowan stage of glaciation: the 
change in the Illinoian surface therefore took place between these two 
glacial stages. Several noteworthy exposures are cited, in one of which 
peat reaches a denth of 13 feet, and in several of which a soil and leacli- 
ing fully equal to that commonly displayed by the Wisconsin or the 
lowan may be seen. A kodak view of one exposure taken at a dis- 
tance of about one-fourth mile shows the Sangamon soil clearly. 
Valley excavation during the Sangamon interglacial stage is touched 
upon briefly. It is shovv^^ that conditions were favorable only for the 
production of shallow valleys, but that these valleys reached in some 
cases a breadth nuich greater than the modern valleys of the same 
streams. Frank Lkverett. 
The Aftonian an'd Pre Kansan Deposits in Soi'thwestern 
Iowa. [Abstract.]! The .Aftonian deposits of southwestern Iowa have 
])eculiar interest in that witliin the area is the typ_e locality for the 
.Aftonian. So far neither the drift of the region nor the Aftonian as' a 
*A. H. Wr.itlien. Geology of Illinois, vol. V, 1873, pp. :«>8-309. 
'•■Roafl before the Iowa Academy of Sciences, Dec. 1897. 
