280 GEOLOGY. 



Orleans. I find, also, that almost any section of our Loess, when 

 saturated with moisture and then frozen and shaved smooth with a 

 knife, will show fine lines of stratification when looked at through 

 a large magnifying glass 



A fact often overlooked is the transition character of some beds 

 of sand, as they shade into the Loess. As beds of Loess and strat- 

 ified sands at the bottom of Loess sections often alternate, und even 

 sometimes with strata of clay, it is not easily conceivable how 

 subaqueous agency should have formed the one and Aeolian agency 

 the other. 



The preceding discussion disposes of the most important objec- 

 tions to the theory of the subaqueous origin of the Loess. The 

 theory of Richthofen is not tenable, in my judgment, for the Ne- 

 braska Loess. I have no doubt that future investigation will show 

 it to be untenable for China. We are now ready to state connect- 

 edly the history of the origin of the Loess. 



True Origin of the Loess Deposits. Geological events have already 

 been traced to the beginning of the Loess period. According to 

 Newberry the whole of the Old Forest Bed area now less than 

 i, 100 feet above the level of Lake Erie was flooded by the changes 

 of level and thawing of retreating glaciers that followed its disap- 

 pearance. In Nebraska during this time icebergs again floated 

 over the waters. The farther retreat of the glaciers and the eleva- 

 tion of eastern Iowa reduced the area of this great lake. What 

 had been a great interior sea of turbulent waters had now become 

 a system of placid lakes that extended from Nebraska and western 

 Iowa at intervals to the Gulf. The Missouri drained through 

 them all along its length. The Missouri, and sometimes the 

 Platte, have been amongst the muddiest streams in the world. If 

 we go up the Missouri to its source, and carefully examine the 

 character of the deposits through which it passes, we cannot be 

 surprised at its character. These deposits being of Tertiary and 

 Cretaceous ages, are exceedingly friable and easy of disintegration. 

 The Tertiary, and especially the Pliocene Tertiary, is largely silic- 

 ious, and the Cretaceous is both silicious and calcareous. In fact, 

 in many places the Missouri and its tributaries flow directly over 

 and through the chalk-beds of the Cretaceous deposits. From 

 these beds the Loess deposits no doubt received their per cent of 

 the phosphates and carbonates of lime. Flowing through such de- 

 posits for more than a thousand miles, the Missouri and its tribu- 



