EROSION PERFORMED BY THE ATMOSPHERE. 331 



watercourses. In northeastern Iowa its distribution shows such 

 remarkable coincidences with the distribution of the primeval 

 forests, as to only leave the uncertainty whether the loess is the 

 cause of the growing of the forest or the forest the cause of the 

 accumulation of the loess. ^ 



J. A. Udden. 

 AuGUSTANA College, 

 Rock Island, 111. 



' See PI. XXII and XLIV, Eleventh An. Rep. U. S. Geol. Survey. McGee. 



