106 Kansas Academy of Science. 



suggests land surface clothed with vegetation offering shelter 

 and food to snails — a vegetation developed under medium con- 

 ditions of moisture and temperature, such as exist here (in 

 Iowa) to-day." 



Mr. Leverett again says, concerning the loess :'" "The north- 

 ern border of the loess, both in western Illinois and in eastern 

 Iowa, appears to have been determined by the ice-sheet. The 

 loess is apparently an apron of silt spread out to the south by 

 water issuing from the ice-sheet. It is loose-textured at the 

 north and is finer textured toward the south, showing a de- 

 crease in the strength of the depositing currents. The wide 

 extent of the loess over uplands has led to a consideration of 

 the influence of wind as well as water in its distribution. The 

 wide extent, however, appears to be due to water distribution 

 rather than wind. Wind action apparently came into force 

 subsequent to the water distribution and is minor in impor- 

 tance." 



Concerning the loess in Wisconsin, Mr. Salisbury says:" 

 "The loess at Devil's lake and at Ableman's, like that in the 

 vicinity of Green lake, was certainly deposited by water, and 

 water associated with the ice of the last glacial epoch. With 

 the loess at Ableman's is to be correlated the clay in the valley 

 of the Balboa and the loams and clays in various other parts of 

 the state. It is distinctly stratified in places, and constitutes, 

 at any rate covers, the valley flats." 



Summary of Opinions Concei-ning the OHgin of the Loess. — 

 The adobe clays of the West and the loess of China are un- 

 doubtedly and universally accepted to be of seolian formation. 

 But the deposits throughout the Mississippi valley are said by 

 Chamberlin, Leverett and others to be in the main a silt forma- 

 tion derived from the ground-up rock-flour of the glacial drift 

 deposits. They further believe that the deposit was laid down 

 in the slow-moving water in the rivers and smaller streams at 

 the foot of the glacier. To this hypothesis, however, there are 

 many objections, some of which are: (a) The loess continued 

 from Wisconsin along the Mississippi to the delta of that 

 stream, {h) The composition of the loess of China and the 

 adobe of the southwestern part of the United States is said to 

 be identical with that of the loess of Iowa, which seems to be 

 good evidence that both were formed in the same way. (c) The 



10. Jour, of Geol., vol. IV, p. 244. 

 17. Jour, of Gcol., vol. IV, p. 929. 



