236 
IOWA ACADEMY OF SCIENCE 
The deposits rest on the Galena-trenton and Maquoketa forma- 
tions which form a peneplain extending from the Niagara escarp- 
ment south of the Turkey river, northward to central Allamakee. 
This peneplain is much cut up by the valleys of the streams tribu- 
tary to the Turkey and Yellow rivers. No valley trains or other 
evidences of outwash are found in any of these valleys except that 
of the Turkey. In fact, drift pebbles or boulders are rare in the 
gravels of these small streams. All exposures are on the high 
ground at the general level of the country, and if the deposits oc- 
cupy the valleys they are nowhere exposed. 
Our observations lead us to believe that a lobe of the Iowan ice- 
sheet extended eastward between the Turkey and Yellow rivers 
to within a few miles of Monona, and that an older one, Kansan 
or sub-Aftonian extended eastward to Waukon, McGregor and 
Garnavillo. 
Only a remnant of this till deposited by the older ice-sheet prob- 
ably now remains on the higher lands, that in the valleys being en- 
tirely carried away by erosion. 
