216 
IOWA ACADEMY OF SCIENCE 
their old characteristics of topographic maturity ; the faces looking 
toward the stream show all the features of extreme topographic 
youth. Some of the qualities of very young streams are here im- 
posed on a very old valley. 
Another notable effect of the loaded Wisconsin floods was the 
building of gravel terraces wherever slack-water conditions were 
present along either margin of the swollen river. Any conditions 
which checked the onward rush of the stream torrent caused the 
load to be thrown down in quantities so large as to be a constant 
surprise to the student of river phenomena. And so now gravel 
terraces are found where the waters evidently whirled and eddied 
and backed up into the mouths of the tributary valleys. The very 
conspicuous deposit (Fig. 4), twenty feet or more in thickness, 
extending up the valley of an insignificant stream in the western 
edge of Lansing, may be cited as an example. Gravel deposits are 
also found wherever the pre-Wisconsin valley had widened out so 
as to leave a low bench or flood plain rising somewhat above the 
level of the main channel. The Peru Bottoms, above Dubuque, 
afford a concrete illustration. Sand and gravel, to a depth of fifty 
or sixty feet or more, are here distributed over hundreds of acres. 
Similar deposits are repeated all along the stream from the mouth 
of the Chippewa southward to Dubuque. Gravels are not common 
below Dubuque, but trains of sand were laid down in large volume, 
wherever conditions were favorable, to points many miles below 
Clinton. In the upper end of Dubuque, toward Eagle Point every 
graded street cuts into an extensive sand terrace. 
Still another event chargeable to the loaded Wisconsin floods was 
the diversion of the Little Maquoketa river from that part of its pre- 
glacial channel between Sageville and the lower end of the city of 
Dubuque. Couler Avenue extends up the old valley to the city 
limits, and the road which continues thence up to Sageville follows 
the pre-Wisconsin trench. Here is an old, well-developed, rock-cut 
river gorge (Fig. 5) , more than a hundred feet in depth, now wholly 
abandoned as a stream course. In the most erratic and unreason- 
able way, apparently, the Little Maquoketa, near Sageville, turns 
away from its old bed and flows northward, seemingly in the wrong 
direction, for about two miles to its present confluence with the 
Mississippi. The swollen Mississippi of the Wisconsin stage seems 
to have divided at the upper end of the Peru bottoms, one swift 
current flowing close to the bluffs west of the bottoms, the other 
following the regular channel. The west current cut into the old 
valley of the Little Maquoketa and used that to its junction with the 
