108 
IOWA ACADEMY OF SCIENCES. 
After the long continuance of such conditions as these, 
the pond became filled with detritus, the water was 
banished from the basin, and during the later portion of 
the Aftonian age this area was again a land surface. When 
the Kansan glacier moved down from the northward it 
carried an immense load of debris. These materials buried 
deeply the old Aftonian surface concealing alike forests and 
peat bog, the stream channels and the bordering hills. 
Since that time a soil mantle has been developed upon the 
Kansan surface, and the streams of the region have carved 
deeply the soft materials of the once level drift plain. In 
some places, as at the point above described, the cutting 
has been so deep as to expose deposits in which are re- 
corded the vicissitudes of earlier geological ages. 
The most of you will remember the pre-Kansan peat 
bed that was exposed at Oelwein, and described for the 
Academy a few years ago by Professor Macbride.* From 
the vegetable material that came from that deposit 
Professor Hclzinger and Dr. G. N. Best have found the 
following species of mosses :f Hypnum ( Harpidium ) 
fluitans Linn., Hypnum ( Harpidium ) revolvens Swartz, and 
Hypnum ( CaUiergon ) richardsoni Lesq. and James. Frag- 
ments of the first named species are much more plentiful 
in the Oelwein deposit than those of all other species 
combined, while in the material from Union county the 
remains of that species are comparatively rare. Concern- 
ing the present habitat of the two latter species Lesquereux 
and James state, in their mosses of North America, that 
Hypnum revolvens occurs in deep swamps from northern 
Ohio to Alaska, and Hypnum richardsoni is reported only 
from British America and the coast of Greenland. 
The peat deposit at Oelwein is of corresponding age with 
that in Union county. Like that of the latter, also, its ac- 
cumulation occupied a long period of time. The plant 
remains which occur in that northern bed bear testimony 
to the same facts as those in the exposure in the more 
southern portion of the State. It seems fair to assume 
* Iowa Academy of Sciences, Vol. IV, p. 63 efc seq. 
t The riryoiogiot, November, 1903. 
