FRESH-WATER STREAMS. 



661 



Again, bedding may result without such changes. The material 

 from successive floods may be of one kind, all of it a fine earth, and 

 yet the deposit be stratified. In the alluvial deposits from a flood, 

 the little layer is begun with a relatively rapid rate of deposition and 

 finished with a slower, as the flood declines, and hence its upper and 

 lower portions will differ as to coarseness and density ; and so with 

 those that follow. 



A wave movement in a lake is sufficient to stratify the falling sedi- 

 ment, since each vibration of the water involves an alternation of ac- 

 tion and comparative quiet. 



If alternations of conditions are absent, a deposit of silt or earth 



Fig. 1093 A. 



Loess formation on the Hoang-ho, in the Province of Shansi, China. 



may be without division into layers. The Jlocculation of particles in 

 fine sediments also tends to make deposits without distinct planes of 

 bedding, as shown by Hilgard. 



The fine earthy terrace-formation of the broader part of large river 

 valleys is often of this character. The loess deposits of the Lower 

 Mississippi and the Rhine (referred to on pages 68, 549, 550, and 559) 

 are examples. While such deposits have no thin layers, like those of 

 ordinary clays, there are usually distant divisions into beds ; and these 

 often become very distinct through the shelves made in it by erosion. 

 The loose material, sometimes several hundred feet thick, is easily cut 

 through by the streamlets or streams the rains make, and the great 

 plains are consequently reduced frequently to a region of pinnacled 

 areas, amphitheatres, and narrow passages, confined by vertical walls, 



