972 Glacial Drift of the Basin of Iowa. 
in which eyes necessarily enter, must have originally had them. 
And, since one finds among them species which are deprived of 
these organs, and which have only traces, hidden and covered, it 
becomes evident that the impoverishment and even the disappear- 
ance of the organ in question is the result of constant disuse. 
[To be continued. ] 
ON THE GLACIAL DRIFT AND LOESS OF A POR- 
TION OF THE NORTHERN-CENTRAL 
BASIN OF IOWA. 
BY CLEMENT L. WEBSTER. 
THE region under consideration may include Floyd county, and 
portions of Cerro Gordo, Worth, Mitchell, Chickasaw, Bre- 
mer, Butler, and Black Hawk counties. The general topography 
of this region is that of a gently undulating prairie country, with 
often a more or less broken surface along the course of the streams. 
Portions of Worth, Chickasaw and Bremer counties are low and 
rather wet, while that of other portions of the area are dryer and 
more rolling. The western portion of this region is drained 
mainly by Flood and Lime creeks and the Shellrock river, while 
the eastern portion is drained by the Cedar and Wapsipinecan 
rivers and their affluents. 
All the streams of the area have a general northwest and 
southeast trend; their initial direction having been predeter- 
mined by the general dip of the subjacent rock strata. The 
Shellrock and Lime creeks have, for the most part, in their 
course through this region, eroded their channels through the 
drift, and into the underlying Devonian strata to a depth varying 
from five to seventy feet. The Cedar has cut through the drift, 
and sunk into the underlying rocks to a depth of from ten feet to 
overone hundred feet. The Wapsipinecan river and Flood creek flow 
through this country mostly upon the drift formation. The valleys 
