Quaternary Geology.— Gordon. pokey 
Upon the last point Salisbury’s statements are greatly at vari- 
ance with those of the majority of previous writers, for he says 
that, in the ‘hundreds of exposures examined for this especial 
purpose, not a single pebble of demonstrably northern origin has 
ever been found.” If the correlation of these beds with the Ter- 
tiary be accepted, and the evidence presented seems conclusive, 
it opens anew the question as to what constitutes the southern 
representative of the drift corresponding to the first episode of 
the first glacial epoch. This is found by the above writers in the 
lower division of the loess, above which is a zone of ozidation 
with traces of an old soil separating it from the later loess above. 
According to this view, it would seem probable that all the de- 
posits above the till at Keokuk should be referred to the loess, 
and if the ferruginous zone corresponds to that giving rise to the 
two-fold division suggested by the above authors, then we have 
the lower division of the southern loess represented here by the 
lower till and the ferruginous division above. An explanation of 
this, however, may be found in the peculiar location of Keokuk 
just within the border of the glacial area. In the retreat of the 
ice sheet to the north there would be deposited first the material 
held by the ice, forming the lower till. But, as the edge of the 
ice receded up the valley, the deposit would gradually change, 
becoming essentially estuarian in character. Then followed a 
period of deglaciation during which, probably, oxidation played 
a prominent part. This constitutes the interglacial episode of the 
earlier glacialepoch. Then came the. closing episode, during 
which, apparently, estuarian conditions prevailed, and the main 
body of the loess was deposited. According to Chamberlain and 
Salisbury this all belongs to the first glacial epoch after which the 
conditions of loessial deposit no more obtain, and the subsequent 
history of these regions is one of continued oxidation, erosion and 
rearrangement, 
In studying this formation we have been specially interested to 
learn if there is any significance in the fact that it is most prom- 
inently developed opposite and for some distance above and below 
the mouth of the Des Moines. In seeking an explanation of the 
probable source of the material constituting it, the agency of that 
river must not be overlooked. For a large part of its course it 
has been cutting its way through the sandstones and shales of the 
Coal Measures, About one hundred miles above its confluence 
