IOWA ACADEMY OF SCIENCES. 205 



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 

 Run 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 Run 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 w^ere 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 disintes'ration. It w^ould 

 seem probable that they were deposited while frozen; 

 otherwise they would surely have been worn away. The flat 



