66 
IOWA ACADEMY OP SCIENCES. 
we recall the notorious fact that peat-bogs and marshes, 
whether by the abundance of humic acid or from other causes, 
are pronouncedly aseptic. If moss, developed under such con- 
ditions, was finally buried at a low temperature and sealed up, 
its preservation is explained. But again, the wood fragments 
referred to are saturated with a solution of ferrous sulphate. 
The occurrence of this salt in this condition is a problem to 
which the attention of the chemist, rather than of the botanist, 
may be invited. 
In closing, one other fact may be mentioned. Some years 
since well diggers of Washington county, in the town of Wash- 
ington, brought up from great depth, some hundreds of feet, 
a perfectly preserved and uninjured cone. This I identified at 
the time as the fruit of Larix americana. If our determinations 
are therefore to be trusted, the Oelwein peat bed and the Wash- 
ington cone represent the same horizon. As the only drift in 
Washington county is Kansan, the position of the Oelwein peat 
as pre-Kansan is to this extent rendered more certain. 
SUMMARY OP DISCUSSION^. 
BY PROP. S. CALVIN. 
The discussion following the preceding papers on the Oel- 
wein section was participated in by Calvin, Fink, Bain, Shimek, 
Beyer, Finch and others. The facts developed during the dis- 
cussion may be summarized as follows: 
A few years ago geologists were content to look upon the 
glacial period as a unit, and the drift mantle of Iowa was 
regarded as the effect of a single invasion and retreat of glacial 
ice. Some time ago, however, McGee demonstrated that in 
northeastern Iowa there are two distinct drift sheets separated 
by a soil horizon and forest bed which represent an interglacial 
period of considerable length. The two sheets of drift were 
then named respectively the lower and the upper till. Later 
two distinct drift sheets were recognized in Union county, near 
Afton Junction. They are separated by a soil bed and by 
motion that Professor Calvin be requested to summarize this discussion was 
carried unanimously. 
