ANIMAL ECOLOGY OF JOHNSON COUNTY 9 
county and spreading to the northeast to include Newport and 
much of Big Grove townships. Portions of Cedar, Graham, and 
Seott, as well as the southern edge of the Clear Creek and Old 
Man’s Creek valleys in Clear Creek, Union, Liberty, Sharon, and 
Washington townships are also too rough for purposes of culti- 
vation. These areas will be more fully treated under the dis- 
cussion of the forest habitats. 
LAKE BASINS 
Remnants of a number of ponds and small lakes may be found 
in the upper half of Madison township. The largest of these, 
Swan Lake, is still nearly half a mile in its largest dimension, 
although it is now little more than a swamp, having been filled 
in by materials carried by rain-wash and by the addition of 
organic matter from the annual death and decay of the many 
plants which flourish in it. Calvin states that at the time of the 
coming of the first settlers, this was a ‘‘beautiful little sheet of 
elear water, twelve to fifteen feet in depth, and well stocked 
with fish.’’ Many of the smaller ponds and lakelets of this 
region have become completely obliterated, although traces of a 
few still remain. Several of the larger ones are indicated on the 
topographical map which was made thirty years ago. According 
to Calvin, these depressions are kettle holes in the drift plain 
along the line where the drift plain and alluvium merge into one 
continuous surface; and it is probable that all of these depres- 
sions had the same origin and were due to the final melting of 
detached ice masses which formed a part of the glacial debris. 
DRAINAGE 
Johnson County is drained by one master stream, the Iowa 
River, with certain smaller areas taken care of by the Cedar 
River and the English River. The latter, however, is a tributary 
of the Iowa and empties into that stream just outside the county, 
in faet just opposite the second tier of sections in Fremont town- 
ship. The watersheds of these areas are indicated on the topo- 
graphical map (Plate II) by a broken line. 
~ The Cedar River drains a small portion of the northeast corner 
of the county, and that stream itself has a course of a few miles 
across the corner of the county. Its basin here comprises a large 
