QUATERNARY AGE. 279 



souri, in its upper portion at least, is not rich in fresh water shells, 

 neither its bottoms nor waters being highly adapted to them. This 

 evidently also was the case with the Loess lake of this region, 

 which was fed, as we shall presently see, by the Missouri and the 

 Platte. I do not adopt the views suggested by Hilgard that the 

 waters of this lake, probably from its alkaline character and the 

 constitution of the Loess itself, destroyed the more fragile shells.* 

 As in the Missouri at the present time, there were comparatively 

 few shells in this old lake. Even a large part of the fresh water shells 

 now found in the Loess were probably carried into this lake from 

 its smaller tributaries. 



Richthofen also claims that the Loess exhibits no marks of strat- 

 ification, and that therefore it could not have been formed by sub- 

 aqueous agencies. In my earlier studies of the Loess it also ap- 

 peared to me to be without stratification. Since my earlier pub- 

 lished papers on this subject, I have found the most convincing evi- 

 dence that the Loess, at least in some sections, is as distinctly strati- 

 fied as the modified Drift beneath it. The following section is 

 given from the new railroad cut at Plattsmouth, to show the hori- 

 zon of stratification. The section is taken from the east end of the 

 cut: 



1. Black soil : 2 feet. 



2. Yellow Loess 10 " 



3. Typical Loess, finely laminated 30 " 



4. Reddish brown, impure Loess, mingled with silicious streaks. . . .15 " 



5. Small boulders, gravel and lime concretions. Small boulders, 



sometimes covered with lime. Some clay. Colors, vaiious. 

 Exposed 6 " 



In this section No. 3 is clearly stratified. A similar laminated 

 appearance is seen in some of the Loess at the west or Plattsmouth 

 end of this cut. In the Republican Valley the lower sections of 

 the Loess are now found to be distinctly laminated and occasionally 

 stratified. Here the strata of Loess are sometimes separated by 

 strata of sand, and even, sometimes, on the upper Republican, 

 by layers of sand and gravel. Similar sections can be seen in some 

 of the canyons through the Loess southwest of Plum Creek. At 

 Plattsmouth, and on the Lower Loup, beds of light are often sepa- 

 rated by beds of darker colored Loess. Along the bluffs of the 

 Republican Valley this condition can be observed for many miles 

 in a stretch. Conspicuous examples can be seen going west from 



* American Journal <>f Science and Art-, for April, 1S79. 



