IOWA ACADEMY OE SCIENCES. 
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suggest stratified rock in places. This formation gradually 
merges into two or three feet of loess soil at the top of the 
section. In places in the formation composed of limestone 
fragments, are inclusions of loess in detached, irregular 
blocks. Most of these are small, but one was observed 
that was estimated as twelve feet long and two and one- 
half feet thick. All the loess masses are irregular and 
sharply separated from the surrounding rock fragments. 
The terrace can be traced for over half a mile; first, a 
short distance east and west in the river valley, then bend- 
ing sharply to the north and fringing the valley of Dry 
Eun on the west. At the end of the terrace next the 
river an exposure shows the limestone fragments of the 
formation underlying the subsoil, to be often as large as a 
foot across; while at the exposure before described, which 
is some distance up Dry Eun from the river, they are not 
more than two or three inches in width. 
Back of the terrace is a loess-covered hill of moderate 
slope, estimated at 75 feet in height. Across the river, 
fully half a mile away, is a terrace opposite the one 
described, and seeming to be at the same level. 
The presence of the loess and soil in the lower half of 
the section described is evidence that antecedent to the 
formation of the terrace, the ground subsequently covered 
by it was dry land above the reach of the river. After- 
wards a stream as large as the Mississippi at Lansing, 
Iowa, flowed through the valley, filling it from bluff to 
bluff. It drowned the mouths of tributary streams and 
backed up their valleys for a considerable distance. Thus 
the layers of sand and gravel were laid; then occurred the 
deposit of the lime-rock fragments, largest in the strong 
waters of the main stream and growing smaller where the 
waters were embayed. Lastly came the rapid recession of 
the swollen waters. 
That the deposition of the terrace was at a rapid rate 
is shown by the burial of the loess fragments in the loose 
rock without any erosion or disintegration. It would 
seem probable that they were deposited while frozen; 
otherwise they would surely have been worn away. The flat 
