378 The American Geologist. December, 1902. 
by erosion of the drift surface during the long intervals be- 
tween the retreat of the Kansan ice and the deposition of the 
loess. On the other hand the valley of the river is older than 
the Kansan ; it is preglacial. There are no indications that this 
part of Iowa was ever occupied by the more ancient ice sheet 
that, over the major portion of the state, preceded the Kansan; 
but that the valley was deep and open almost as it is to-day 
when the ice of the Kansan stage was melting, is attested by 
terraces of rusty Buchanan gravel at various points along the 
stream. A concrete illustration of these old gravels, deposited 
bv floods from the melting Kansan ice and rising not more 
than twenty or twenty-five feet above the level of the water 
in the present channel, is found south of the bridge at Flor- 
enceville, near the center of section 10, Albion township. 
The loivan Area. — The lowan area embraces much the 
larger part of Howard county. There was a time, however, 
when the whole county, and practically the whole surface of 
Iowa, presented an appearance topographically like the north- 
eastern part of Albion township. At a date very recent com- 
pared with the age of the Kansan drift, glacial conditions re- 
curred ; a new ice sheet coming from the northwest flowed 
over the eroded Kansan surface, obliterating the old erosional 
topography as far as it went, distributing new and fresh ma- 
terial, and leaving the surface, when the ice melted, in the 
form of plain with long, low, sweeping undulations. Con- 
structive work of glacier ice in spreading out and piling up 
morainal detritus, was the potent factor in developing the re- 
sulting topography. Erosion was in no way concerned. Eros- 
ion has had practically no effect in modifying the ice-moulded 
surface of the lowan drift since the disappearance of the Io\y- 
an ice. 
lowan glaciers covered all of Howard county except the 
few square miles of the Loess-Kansan area already described. 
The lowan ice advanced to what is now the .boundary line be- 
tween the two topographic areas of the county, and there 
stopped. On one side of that line the topography is old, on 
the other side it is young. Along the boundary line there is 
usually a great thickening of the loess ; and as ordinarily seen 
from the lowan plain the margin is marked by a series of hills 
which, from a distance, present the appearance of a terminal 
