THE PLEISTOCENE OR GLACIAL PERIOD 889 



would not regard them as loess. Some, indeed, would so define 

 loess as to make it an eolian product. 



By the aqueous hypothesis, the loess is assigned to direct depo- 

 sition by rivers, or their lake-like expansions. To make this pos- 



Fig. 592. Loess Shells, a-b, Zonitoides minusculus (Binney); c-d, Euconu- 

 lus fulvus (Drap.); e-f, Strobilops labyrinthica (Say); g, Polygyra clausa 

 (Say); h, P. multilineata (Say); i-j, Succinea obliqua Say; k, S. avara 

 Say; l-m, Polygyra monodon (Rack); n, Bifidaria pentodon (Say): 

 o, B. corticaria (Say); p, B> muscorum (Linn.); q, B. armifera (Say). 

 The small figures adjacent to some of the large ones show the natural 

 size of the shells. 



sible it is necessary to suppose that the waters stood at elevations 

 200 to 600 feet higher than now, relative to adjacent surfaces, in 

 the Mississippi basin. This involves difficulties that have never 

 been satisfactorily met. Furthermore, if the waters of rivers or 



