IOWA ACADEMY OF SCIENCES. 45 



remained covered with sedges and grasses for a time, bat 

 these too yielded to the sand-bar willow, which now 

 extends quite to the waters edge. These terraces of veg- 

 etation may now be observed: the sand bar willows in the 

 foreground; beyond them and rising above them, the taller 

 black willow, white ashes and cotton woods: and in the 

 background the still taller elms, cottonwoods and other 

 trees of the old alluvial plain. These three terraces of 

 plants correspond to three terraces of soils, two of them 

 bnilt up out of a river bed within twenty-five years. 



The beds of the lakes and ponds which were left by the 

 retreating glaciers were also gradually covered with an 

 accession of floras, each of which accumulated more soil, 

 partly from waters and partly from winds, and thus pre- 

 pared the way for its successor Such gradation of floras 

 is still shown along some of the lakes and swamps within 

 the Wisconsin drift lobe, and is illustrated in Plate XL 

 These lakes and ponds were formerly so abundant in the 

 northern part of the Wisconsin lobe that that region was 

 known to the early settlers as the "thousand lake region 

 of Iowa," but within twenty years most of them have dis- 

 appeared, and their beds are now covered with vegetation, 

 native or introduced. Even the very wfit season of 1902 

 w^as able to restore only a comparatively small number of 

 these former lakes. 



But not all soil has accumulated from water. Indeed, 

 a very large part of it seems to have been carried to its 

 present location by winds, and again plants served as hold- 

 fasts. The powerful influence of winds is demonstrated 

 constantly in the sand hills of Muscatine Island, and of 

 Nebraska, in the sand dunes of Lake Michigan, and by the 

 dust storms along the Missouri river. Large quantities of 

 material are transported by winds. In the northern part 

 of West Point, Nebraska, several exposures show sand 

 which has been carried over genuine loess, in one place to 

 a height of sixteen feet. The writer was present when the 

 roadway leading to the Bohemian cemetery in West Cedar 

 Rapids, Iowa, was being graded. The excavation, which 

 was made at the top of the high ridge, revealed a fence 



