414 THE ICE AGE IN NORTH AMERICA. 



A noticeable phenomenon west of the driftless area in 

 Wisconsin and Iowa is that the loess is thickest near the east- 

 ern margin of the ice-lobe which passed southward through 

 central Iowa. The distance from the driftless area to the 

 Missouri River, or the width of this lobe in the latitude of 

 Milwaukee, is not far from three hundred and forty miles. 

 It is urged that the presence of an ice-lobe over that region 

 may have had influence in elevating the loess deposits. Since 

 attraction varies inversely as the square of the distance, such 

 a mass of ice near at hand would slightly raise the water along 

 its margin. The objection to this is that the wider ice-lobe 

 to the east did not produce corresponding influence. 



Among the more fruitful supplementary hypotheses 

 brought in to aid in the solution of this part of the prob- 

 lem is to be mentioned that of glacial dams similar to those 

 already alluded to in Europe. In this country the principal 

 held in which they may have existed is where it is most 

 needed, namely, west of the Mississippi. An examination 

 of our map will at once suggest that it is possible for much 

 of the loess in northeastern Kansas and eastern Nebraska to 

 have accumulated in temporary lakes formed by glacial dams 

 across the mouth of the Kansas and Platte Rivers, or even of 

 the Missouri itself. How far this cause may have operated 

 remains yet to be determined. 



So complicated are the facts pertaining to the loess as 

 they now appear, that it is not likely that, for some time to 

 come, investigators will arrive at a perfect agreement con- 

 cerning its manner of deposition. Those, however, who 

 have most attentively studied glacial phenomena may be par- 

 doned if they work the glacial hypothesis for all that it is 

 worth. The existence of the vast body of ice which covered 

 the glaciated area introduces a very complicated and efficient 

 cause which it is exceedingly difficult to eliminate from the 

 problem ; and it is as allowable for the glacialist to take 

 refuge in supposed ice-dams, where their existence is possible 

 and can not be disproved, as for the ordinary geologist to sup- 

 pose vast orographic changes. The study of the loess has 



